Philosophers have used the term 'consciousness' for four main topics: knowledge in general, intentionality, introspection (and the knowledge it specifically generates) and phenomenal experience (sections 1-2). This entry discusses the last two uses (see other entries on the former two). Something within one's mind is 'introspectively conscious' just in case one introspects it (or is poised to do so). Introspection is often thought to deliver one's primary knowledge of one's mental life. An experience or other mental entity is 'phenomenally conscious' just in case there is 'something it is like' for one to have it. The clearest examples are: perceptual experiences, such as tastings and seeings; bodily-sensational experiences, such as those of pains, tickles and itches; imaginative experiences, such as those of one's own actions or perceptions; and streams of thought, as in the experience of thinking 'in words' or 'in images'. Introspection and phenomenality seem independent, or dissociable, although this is controversial (section 6).
Phenomenally conscious experiences have been argued to be nonphysical or at least inexplicable in the manner of other physical entities. Several such arguments allege that phenomenal experience is 'subjective', that understanding some experiences requires undergoing them (or their components). The claim is that any objective physical science would leave an 'explanatory gap', failing to describe what it is like to have a particular experience and failing to explain why there are phenomenal experiences at all (section 3). From this, some philosophers infer 'dualism' rather than 'physicalism' about consciousness, concluding that some facts about consciousness are not wholly constituted by physical facts. This dualist conclusion threatens claims that phenomenal consciousness has causal power, and that it is knowable in others and in oneself (section 4).
In reaction, surprisingly much can be said in favour of 'eliminativism' about phenomenal consciousness, the denial of any realm of phenomenal objects and properties of experience (section 5). Most (but not all) philosophers deny that there are phenomenal objects - mental images with color and shape, pain-objects that throb or burn, inner speech with pitch and rhythm, etc. Instead, experiences may simply seem to involve such objects. The central disagreement concerns whether these experiences have phenomenal properties - 'qualia', particular aspects of what experiences are like for their bearers. Some philosophers deny that there are phenomenal properties - especially if these are thought to be intrinsic, completely and immediately introspectible, ineffable, subjective, or otherwise potentially difficult to explain on physicalist theories. More commonly, philosophers acknowledge qualia of experiences, either articulating less bold conceptions of qualia, or defending dualism about boldly conceived qualia.
Introspective consciousness has seemed less puzzling than phenomenal consciousness. Most thinkers agree that introspection is far from complete about the mind (section 7) and far from infallible (section 8). Perhaps the most familiar account of introspection is that, in addition to 'outwardly perceiving' nonmental entities in one's environment and body, one 'inwardly perceives' one's mental entities, as when one seems to see visual images with one's 'mind's eye'. This view faces several serious objections (section 9). Rival views of introspective consciousness fall into three categories, according to whether they treat introspective access (1) as epistemically looser or less direct than inner perception, (2) as tighter or more direct, or (3) as fundamentally nonepistemic or nonrepresentational (section 10). Theories in category (1) explain introspection as always retrospective, or as typically based on self-directed theoretical inferences. Rivals from category (2) maintain that an introspectively conscious mental state reflexively represents itself, or treat introspection as involving no mechanism of access at all. Category (3) theories treat a mental state as introspectively conscious if it is distinctively available for linguistic or rational processing, even if it is not itself perceived or otherwise thought about.
As elsewhere in philosophy, Descartes's writings mark a major shift in philosophical preoccupation with consciousness. Pre-Cartesian philosophers of mind rarely emphasize the terms 'conscious' or 'consciousness' (or clear equivalents). Post-Cartesian philosophers of mind rarely avoid such emphasis. This section compares Descartes's usage with earlier usage, and the next section discusses subsequent ideas.
Descartes typically speaks of being 'conscious' to refer to an allegedly intimate source of knowledge about one's own mental occurrences. In the Conversation with Burman he says that 'to be conscious is both to think and to reflect on one's thought' (1648, vol. III, p. 335), where the term 'thought' extends widely, as in the Second Replies, to 'everything that is within us in such a way that we are immediately conscious of it' including 'all the operations of the will, the intellect, the imagination and the senses' (1641, vol. II, p. 113). Descartes seems to treat everything mental as introspectively conscious, in these passages and elsewhere (see the Fourth Replies, 1641, vol. II, p. 171). Elsewhere, however, Descartes seems to deny that introspection is complete, as in the Discourse on Method: 'many people do not know what they believe, since believing something and knowing that one believes it are different acts of thinking, and the one often occurs without the other' (1637, vol. I, p. 122).
The resulting focus on the scope and limits of introspective knowledge (see sections 6-7) is apparently responsible for the modern uses of 'conscious' and 'nonconscious' to mark a potential distinction between two kinds of mental states. Introspected states are (introspectively) conscious, while others, if any, are (introspectively) unconscious. Pre-Cartesian authors do not use the word 'conscious' to mark such a distinction, although some may be committed to the distinction, either implicitly or in other terms (Whyte, 1962). To take a rather spectacular example, Socrates claims in Plato's Meno that since one's soul 'has been born many times' and 'has learned everything that there is', 'seeking and learning are in fact nothing but recollection' (1961, p. 364; 81c-d). This seems to require that one has latent knowledge of which one can at best become aware with great difficulty.
Many pre-Cartesian writers share commitment to a special fountain of reflective knowledge, often called 'inner sense'. In Summa Theologica Aquinas posits a 'common sense' which enables one for example to 'tell white from sweet', and adds that this common sense 'is also able to sense sensation itself, as when somebody sees that he is seeing' (1273, pp. 228-9; 1, 78, 4). This responds to Aristotle's apparent claim, in De Anima, that it is 'by sight that one perceives that one sees' rather than by another sense (1968, p. 47; III, 2, 425b12). On these views, the subject matter of such inner awareness is more restricted than for Descartes, including sensation but perhaps not other mental processes. It may even be that for Aristotle, the relevant 'inner' perception - by which one sees that one sees - is directed at one's external sense organs themselves and not at anything Descartes would consider strictly 'mental'.
A nearer equivalent to 'introspective consciousness' is the Sanskrit term 'manas,' used widely in Hindu texts for a 'mind-organ' that functions like the external sense organs (Smart, 1964). For instance, the Vaisesika Sutra (ca. 3rd century BC) claims that '[i]ntellect, pleasure, pain, desire, aversion, effort are perceptible by the internal organ' (Radhakrishnan and Moore, 1957, p. 411). This inner perception is carefully distinguished from 'inferential knowledge', and is framed so as not to involve introspection of a 'self'. Indeed, while Descartes holds that he can introspect himself as a 'thinking thing', Hinduism characteristically claims that introspection reveals no 'true self' distinct from one's mental states, and Buddhism characteristically denies that there are 'thinking things' at all (see INDIAN PHILOSOPHY).
The word 'conscious' derives from the Latin words 'cum' ('together with') and 'scire' ('knowing'). In the original sense, two people who know something together are said to be conscious of it 'to one another', with the irresistible connotation that they are privy to a scandalous secret. By extension, one can be conscious 'to oneself' of secret shames - whence the original use of 'consciousness' for conscience, the inner accuser silently sharing knowledge of one's transgressions. This archaic moral sense of 'consciousness' is not a concern in this entry (see CONSCIENCE).
The Latin conjunction of 'cum' and 'scire' also has a use in which the prefix is merely emphatic, so that being 'conscious of' something simply means knowing it, or knowing it well. In this sense the word 'conscious' can also be used as an adjective: a 'knowing' being such as a normal person is a conscious being, while an 'unknowing' being such as a plant or sleeping person is an unconscious being. 'Conscious', like 'knowing', can be used in this way for things with minds but not for things within minds, such as mental states. People and animals know things - are conscious of things - but mental states do not themselves know things. Thus, for example, Aquinas uses 'conscious' to describe bearers of mental states - such as human beings, animals, and God - but not to describe mental states - not even 'seen' seeings. Since the main philosophical problems about consciousness concern the more modern distinction between conscious and unconscious states, this entry focuses neither on the distinction between conscious and unconscious subjects, nor on the broad 'knowing' sense of 'conscious' (see KNOWLEDGE, EPISTEMOLOGY). In effect, Descartes refashions the 'knowing well' sense of 'conscious', regimenting it for a particular source of knowing, introspection. Issues about the specific epistemological status of introspection are a central concern of this entry.
Descartes's use of 'consciousness' for reflective knowledge spreads rapidly through the next generation of European philosophers: in An Essay concerning Human Understanding Locke writes, as he does of 'reflection', that '[c]onsciousness is the perception of what passes in a Man's own mind' (1689, p. 115; II, I, 19) while Leibniz recommends in The Principles of Nature and Grace, based on Reason that 'it is well to make a distinction between perception, which is the inner state of the monad representing external things, and apperception, which is consciousness or the reflective knowledge of this inner state itself' (1714, p. 637). Kant goes on in Critique of Pure Reason to distinguish between 'empirical apperception' of a 'flux of inner appearances' - mentioning that '[s]uch consciousness is usually named inner sense' - and 'transcendental apperception' which is alleged to be a 'pure original unchangeable consciousness' that reveals a 'fixed and abiding self' (1787, p. 136; A 107). This entry discusses one's introspective access to the 'flux' of particular events within one's mind, rather than substantive introspective knowledge about one's self - about whether one is made of physical or spiritual components, and whether one persists through time (see SELF-KNOWLEDGE, PERSONAL IDENTITY).
In the broader 'knowing' sense (see section 1), a creature is conscious of something just in case it knows something, independently of whether this knowing is itself introspectible. This ancient sense of 'conscious' lingers on, and broadens to cover any kind of belief or cognition (whether or not it is 'knowledge'), and any kind of attitude about something (whether or not it is 'cognitive'). In this sense, a creature has consciousness if it has any kind of 'intentional' mental state. By extension, the state itself can be said to be a state of consciousness, even if it is not introspectible. (This is distinct from the widespread claim that all conscious states are intentional - that 'all consciousness ... is consciousness of something' (Sartre, 1943, p. 11). On this broad sense of 'conscious', by definition, all 'ofness' is conscious ofness.) As twentieth-century philosophers of mind and language most often pursue concerns about intentionality using terms other than 'consciousness', intentionality will not be explored in this entry (see INTENTIONALITY, MEANING).
In a still broader sense, 'mind' and 'consciousness' are synonyms, as are 'being mindful of' something and 'being conscious of' it, so that any kind of mental state (whether or not it is an 'attitude') is a state of consciousness. When Hegel, Marx or Lukacs speak of 'unhappy', 'false' or 'class' consciousness, or when political activists attempt to 'raise' consciousness, their concerns are usually equally well rendered using a general term such as 'knowledge', 'thinking', 'attitudes', or 'mentality' in place of 'consciousness'. It is not clear that their concern is with introspection, since they refer mainly to thoughts about (or seemingly about) nonmental things, independently of whether these thoughts are themselves introspectively conscious. (When Hegel refers to thoughts explicitly about the mind, he uses 'self-consciousness' rather than 'consciousness'.) Likewise, many scientific writings officially on 'consciousness' are about mentation and mentation-like activity in general, avoiding any question of whether the activity is introspectively unconscious. Since these broad uses of 'consciousness' seem to introduce no distinctive philosophical perplexities, this entry puts them aside (see MIND, PSYCHOLOGY).
With the dawn of scientific psychology in the late nineteenth century, the central philosophical controversies about consciousness center around whether consciousness can ever be explained by an objective science of the mind. The biologist Thomas Huxley provides an early attempt to express the sense of mystery: 'How it is that anything so remarkable as a state of consciousness comes about as a result of irritating nervous tissue, is just as unaccountable as the appearance of Djin when Aladdin rubbed his lamp' (1866, p. 210). Since that time there have been many scientific advances in understanding the mechanisms of perception, thought, and communication, and many philosophical advances in understanding the nature of intentionality and meaning. According to Thomas Nagel and many other philosophers, such advances must leave an unexplained residue, concerning what it is like to have phenomenally conscious experiences (as illustrated in the introduction). Nagel writes that '[c]onsciousness is what makes the mind-body problem really intractable', identifying 'subjectivity' as its most troublesome feature:
Until quite recently, the agenda for the philosophy of mind has been set more by epistemology than by the sciences of mind. Consequently, introspective consciousness has been the most central and important philosophical notion of consciousness. The remainder of the entry is divided between the explanation of phenomenal consciousness and the epistemology of introspective consciousness.
Nagel argues that physical theories cannot explain one's phenomenal consciousness, because they abandon one's point of view (see section 2). Science does indeed abandon one's point of view, insofar as one need not be able to understand or defend the theory (if one lacks relevant concepts or evidence), and insofar as subjects with other points of view should be able to understand and defend the theory. But does abandoning a point of view prevent describing the point of view, or the features viewed from that point? Even if Nagel is correct that one's point of view and one's phenomenal experience are 'essentially' connected, they may not be exclusively connected. An objective physical theory of phenomenal consciousness would presumably allow that phenomenal features are accessible from multiple points of view - for instance, both by some form of introspection and by some form of neurophysiological or psychological observation and theory. Furthermore, if experiences are necessarily introspectible or introspected (see section 6), this might explain Nagel's claim that phenomenal features are 'essentially connected with a single point of view'.
Frank Jackson (1982) amplifies Nagel's challenge in his 'knowledge argument' against 'physicalism', the thesis that the world is wholly physical. He imagines a super-scientist, Mary, who has never seen anything coloured, because she lives her life in a black-and-white room. From a black-and-white television in this room, she learns all the objectively specifiable physical (and causal or 'functional') facts in the world. When she finally leaves the room and first sees colour, Jackson argues, she learns a new fact about the nature of phenomenal experience; she might exclaim, 'Oh! It is like this to see red!' The new fact Mary learns cannot be identical to a physical or functional fact, or else it would be among the facts Mary already knows before leaving the room. So no wholly physicalist account of phenomenal facts can be true.
Most responses to Jackson's argument involve denying that Mary learns a new fact upon experiencing red (for a review, see van Gulick, 1993). On some views, she learns how to do new things - to imagine experiencing redness or to recognize redness visually - without coming to know that any new fact obtains. On others, she learns that an old physical fact about experience obtains, but comes to know it in a new way - via introspective access or via new concepts. For example, one proposal compares the relevant introspective ways of representing one's experiences with simple inner-perceptual demonstratives (see Lycan, 1990), ways of knowing colour experience that would be unavailable to Mary from within the black-and-white room. Consider an analogy: when one perceives a banana and thinks of it demonstratively - as 'this' - those who do not perceive the banana cannot think of it in the same way - simply as 'this' (while staring at something else). Likewise, if one's introspections of one's experiences involve some demonstratives of them, this would explain why these representations cannot strictly be shared by someone who does not 'perceive' the same experiences but merely thinks about them. (For marks against this strategy, see Raffman, 1995; for further elaboration, see Tye, 1995, pp. 173-8.)
Even among philosophers who accept that phenomenal consciousness is some physical or functional process, there are doubts about the possibility of explaining it. Colin McGinn (1991) suggests that human beings are forever blocked from knowing the 'link' between the brain and consciousness, roughly because introspective consciousness gives no knowledge of brains, while neuroscientific access to brains gives no access to consciousness. Critics respond that one might learn the explanatory link by theoretical inference from joint introspective and scientific data, such as correlations between phenomenal features and brain states (see Flanagan, 1992, ch. 6).
In slightly different ways, Joseph Levine (1993), Jackson (1993), and David Chalmers (1996) argue that even if one can know what this 'link' in fact is, explanations based upon it cannot be as satisfying as other scientific explanations. In essence, the argument is that for any objective, scientific account of phenomenal consciousness, one can conceive of a creature that meets the conditions in the account but lacks phenomenal consciousness. In the extreme case, it is said, one can conceive of a world that is an exact physical duplicate of the actual world - complete with duplicate stars, planets, rocks, plants, animals, and philosophers - but which lacks any phenomenal consciousness. All the human-like beings in that world would be nonphenomenal 'zombies'. So the prescientific concept of phenomenal consciousness is not such that scientific premises could necessitate, a priori, conclusions about the phenomenal. In Levine's terms, there is an 'explanatory gap' between physical reality and phenomenal consciousness. By contrast, for example, it is claimed that the prescientific concept of water is such that scientific premises about H2O, can necessitate, a priori, conclusions about water. In particular, it is held to be part of our concept of water that if there is anything roughly unique in the lakes and rivers around us that has a preponderance of features such as boiling, eroding rocks, quenching thirst, etc., then it is water. If science establishes that H2O meets this condition, then there is no further conceptual possibility that H2O is not water.
At least three lines of response may be advanced against the explanatory gap argument. One concedes that no scientific premises a priori necessitate conclusions about the phenomenal, but insists that the same is true for scientific explanations of water, etc. Perhaps someone who believes in water but denies that it boils, is in lakes, etc. is making a false and bizarre claim but is not strictly contradicting himself. The fate of this response presumably depends on the fate of general reservations about a priori or conceptual necessity (see A PRIORI).
The second strategy also concedes the lack of a priori necessity, but attributes it to the idiosyncratic ways in which phenomenal facts are represented - e.g., by introspection-based demonstratives (Tye, 1995, pp. 178-181). By comparison, suppose that agent A holds banana B in front of his face, and comes to accept the demonstrative 'this is a banana'. This conclusion cannot strictly be deduced from any demonstrative-free descriptions of the banana - that B is a banana in A's hand, that A sees B, etc. The subject could believe all of these premises, and still conceive that this is not a banana - perhaps by conceiving that he is not in fact agent A (see DEMONSTRATIVES). This response to the explanatory gap seems at best to apply only to particular phenomenal conclusions, of the form: it is like this to have a given experience. It is an incomplete response, since there are phenomenal conclusions without demonstratives, namely, those of the form: there is something it is like to have a given experience.
The third strategy is to deny that there is an unbridgeable conceptual gap; in effect, to deny that zombies (nonphenomenal physical duplicates of phenomenal creatures) are even conceptually possible. In Nagel-like fashion, Robert Kirk analyzes the concept of phenomenality as follows: a creature's phenomenal states are those with different 'characters' that are 'for the creature as a whole' (1994, ch. 5). He explains this in terms of neural states with different 'patterns of activation' that are 'directly available' to 'have different effects on processes of assessment, decision-making, and action initiation'. It follows that if a creature has states with characters for the creature, any physical duplicate of the creature does also. The problem is that Kirk's 'having character' does not express the same concept as Nagel's 'being like something'. Perhaps Kirk demonstrates how states can be 'for a creature', but he does not demonstrate that they are 'like something' for the creature, i.e., phenomenal, in Nagel's full-blown sense. For example, beliefs may also be realized in different patterns of activation with the relevant direct availability, and so in that sense beliefs may be 'for' a creature, but beliefs are not clearly themselves 'like something' for a creature (see section 6). Further analysis of the 'like something' idiom would be needed to complete this line of response to the explanatory gap.
The attraction of subjectivity-based arguments against physicalism makes it important to understand the potential ramifications of various nonphysicalist alternatives. The central metaphysical issues concern 'mental causation' and 'emergence' (see CAUSATION, MIND–BODY PROBLEM). The two central epistemological ramifications concern knowledge of other minds and knowledge of one's own mind (see OTHER MINDS, SELF-KNOWLEDGE).
Physical science promises an explanation of physical events wholly in terms of other physical events. For example, unsupported objects fall, not because they want to fall, but because of gravitational forces. Similarly, a large group of neurons cause another neuron to fire, not because of its embarrassment due to peer pressure or its fear of a mob, but because of electrochemical forces. In this way, there should be a purely physical explanation of the activities of brains in producing (reflex or nonreflex) behavior. Yet phenomenal consciousness also seems to have physical consequences on behavior. When one feels an itch, one scratches; this seems to be in large part because of what it is like to itch. But how can an itchy feel make a difference, if there is a purely physical explanation of one's hand motions? The physicalist may make room for phenomenal causation by maintaining that the feel of an itch is wholly constituted by (or, perhaps, identical with) features of the brain and body. The feel causes the hand-motion, because it is made of things that do so, just as the brain causes the hand-motion by being composed of things that do so (i.e., neurons). But this strategy is unavailable to the nonphysicalist who thinks there are mental objects, properties, or states that are not wholly composed of physical entities. One possibility for the dualist is to maintain that some physical events are inexplicable purely in physical terms - this is Descartes' own position about nonreflex behaviour. Another prominent strategy is to defend 'epiphenomenalism' about the phenomenal, or the idea that, contrary to appearances, phenomenal features are irrelevant to the generation of physical events (Jackson, 1982; Chalmers, 1996, ch. 4).
If phenomenal states and features are not wholly constituted by physical states and features, how are they constituted? One idea, prevalent among neuroscientists, is that the phenomenal 'emerges' from physical interactions. By analogy, water has properties that are not explicable by the properties of hydrogen and oxygen separately. Water dissolves salt, but neither hydrogen nor oxygen do so separately (nor does hydrogen dissolve part of salt and oxygen the rest). Analogously, the whole of a phenomenal experience is taken to be more than the sum of its physical parts (i.e., the physical entities that help realize it). The initial plausibility of such analogies seems to depend on a too-narrow conception of the 'parts' of a complex entity. A water molecule does have hydrogen and oxygen atoms as parts, but it also has various relations among these atoms as other 'parts'. The physical relation of bonding, for instance, is as necessary for water as the atoms are. If all of the parts of water are counted, it is not clear that water has properties inexplicable by the properties of these parts. This kind of 'emergence' conclusion - one that forgets to 'sum' some of the parts of a whole - is compatible with a wholly physicalist account of water, and of consciousness. In the absence of better analogies, nonphysicalist philosophers have more commonly denied that there is genuine emergence, emergence of new features that are inexplicable in terms of combinations of other features. This leads some nonphysicalists to the startling 'panpsychist' claim that mental 'ingredients' of phenomenal consciousness must be present in the tiniest bits of matter capable of comprising brains, and to the claim that phenomenal consciousness is a fundamental part of nature - perhaps along with subatomic mass and charge (Nagel, 1979; Chalmers, 1996, ch. 8).
Epiphenomenalism and panpsychism exacerbate the epistemological problem of other minds, but in opposite directions. It seems that one has excellent, even if not quite perfect, justification for believing that other people have experiences. Plausibly, talk of experiences is not simply disguised talk of others' observable behaviour, but is instead to be inferred from behaviour with some degree of theoretical risk (Putnam, 1963). Perhaps the inference is in part grounded on drawing an analogy between oneself and others, but inference from a single case gives one at best meager justification for conclusions about others. The residual problem of other minds, then, is to explain how one attains an appropriate level of justification. The physicalist can maintain that one is justified in part because the phenomenal features of experience help explain behaviour - in fact, help cause it. But the epiphenomenalist seems forced to deny this, potentially rendering it too hard to attain knowledge of other minds. The panpsychist, on the other hand, renders it too easy to attain such knowledge; not only other people but other animals, plants, rocks, and protons have mental features.
A final danger with the idea that phenomenal consciousness depends on nonphysical features is that it threatens self-knowledge about one's phenomenal states. The nonphysicalist who believes that zombies are possible believes that two people could be alike in all nonphenomenal respects, while one has phenomenal experience and the other does not. Each could be fully convinced of his own rich, detailed phenomenal experience, but one would be wrong. It is difficult to see how either could justify his belief that he is not a zombie, if zombies are possible. Chalmers tries to address this problem by stipulating that nonzombies are necessarily distinctively justified:
This conclusion anticipates the idea that inner-perceptions of one's experiences - taken to be more 'primitive' than reflective beliefs about one's experiences - are necessary for phenomenal consciousness (see section 6). But where the nonzombie has inner-perceptual states, by hypothesis the zombie has them also. Perhaps what the zombie has are misperceptions, but this need not lessen his justification in accepting them at face value, and in believing he has experiences.
Also, the heavy reliance on introspections of experience opens up two alternatives for physicalism. The first is to deny that there is experience at all, but only the favored kind of introspections as of experience. The second - perhaps the more attractive - is to maintain that the favored kind of introspections are sufficient for experience. This is to invert Chalmers' claim that 'to have the experience is to be related to it in this [inner-perceptual] way'; if so, this is precisely because to be related to a state in this inner-perceptual way is to have an experience. Neither strategy carries obvious commitment to anything nonphysical. (For related objections to 'absent qualia', see Shoemaker, 1984, chs 9 and 14; and for a response, see Block, 1980. Rey, 1986, extends the point, arguing that non-psychological requirements on phenomenal consciousness - perhaps biological or neurophysiological ones - would also jeopardize introspective knowledge of experience; see also Chalmers, 1996, ch. 7.)
In addition to subjectivity-based arguments, phenomenally conscious experiences provide other interesting arguments against physicalism. In certain experiences one seems to be aware of phenomenal denizens of an inner mental world: coloured and shaped mental 'images', bodily 'sensations' such as 'pains' that may be throbbing or in one's limb, and inner 'speech' with 'private' volume and pitch. Such alleged mental objects as afterimages, pains and inner speeches, that are naturally reported as having properties of nonmental objects (e.g., roundness, throbbingness or loudness), may be called 'phenomenal objects'. The argument against physicalism based on reports of phenomenal objects is simple. In such experiences nothing in one's brain or body or (causally relevant) environment is literally purple and round, literally throbbing and in a limb, or literally soft and medium-pitched. So if phenomenal objects do exist with these properties, they are not among the things in one's brain or body or environment. One must be either a dualist (see section 4) or an 'eliminativist' about mental entities with these properties; that is, the physicalist must deny that objects with such properties exist.
The challenge for the eliminativist about phenomenal objects is to explain why people are often tempted to claims of phenomenal objects, with ordinary perceptible properties. Broadly, the temptation may be attributed to an ambiguity or looseness in ordinary reports of experiences, or to an illusion built into the experiences themselves, which may then be reported strictly and faithfully. Ned Block (1983; see also Tye, 1995) pursues the former strategy by pointing out that people often describe representations as having properties that they merely represent: the phrase 'a warm thermostat setting' may be used for a thermostat setting of warmth, and 'a nude painting' may be used for a painting of nudity. It should be no surprise then that people describe experiences of colour and shape as themselves being coloured and shaped, and so no surprise that, speaking freely, they treat them as images. The other strategy is latent in J. J. C. Smart's suggestion that '[t]here is, in a sense, no such thing as an after-image . . . though there is such a thing as the experience of having an image' (1959, p. 151). On one straightforward construal of 'the experience of having an image', an experience itself represents that there is an image with certain features, although there is no such thing (cf. Sartre's 'illusion of immanence', 1940, p. 5). The illusory-experience view has an advantage over the reporting-based view to the extent that afterimages look purple and round, pains feel dull or in motion, and inner speech seems to sound faint or high-pitched. By contrast, a warm thermostat setting need not itself feel warm, and a nude painting need not itself look nude (any more than other paintings look clothed). However, without an account of why experiences misrepresent phenomenal objects, the illusory-experience view does not adequately discharge the eliminativist's explanatory burden (for one account, see Rey, 1997).
In addition to phenomenal objects, eliminativists have targeted alleged 'phenomenal properties' of experiences, or 'qualia'. There is not merely 'something' it is like to have a phenomenally conscious experience, but some particular 'thing' or things it is like. People sometimes try to describe these particular properties, for example, by saying that a given pain is 'sharp' or 'throbbing' to some degree, or that a given visual image is 'blurry' or 'moving'. Even if the eliminativist about phenomenal objects is correct that there are only experiences as of sharp, throbbing pains and as of blurry, moving images, descriptions such as 'sharp' and 'blurry' seem in some indirect or nonliteral way to convey particular aspects of what it is like to have these experiences. In a relatively cautious use of the word 'qualia', particular what-it-is-like properties, whatever their nature turns out to be, are qualia.
There are bolder uses of 'qualia' on which the word can apply only to properties of experience that pose challenges to scientific explanation. Some require qualia to be infallibly and completely accessible to introspection, which is puzzling on any plausible scientific explanation of introspection (see sections 6-8). Some require qualia to be inaccessible without introspection - for instance by purely behavioural or neurophysiological tests that one may perform on other people, without relying on an introspective understanding of one's own experience; this seems to preclude explanation of qualia as physical properties discoverable in multiple objective ways (see section 3). Perhaps the most controversial philosophical idea about qualia, however, is that they are 'intrinsic' properties of experience. Metaphysicians dispute the correct account of intrinsicality, but the following may serve to convey the intuitive idea, as it applies to experience: for an experience to have a property intrinsically, the experience must have the property solely in virtue of the spatiotemporal parts of what realizes the experience. (This is meant to exclude everything that even in part exists when or where the experience does not, for example, stimuli that cause the experience, and behaviour and other mental states that the experience causes.) This seems to preclude explaining qualia in 'functionalist' terms by appeal to the causal role of experiences, or in 'intentionalist' terms by appeal to the representational content of experiences. Defenders of the intrinsicality of qualia often argue for the possibility of 'inverted qualia', cases in which two experiences differ in qualia even though they have identical causal or representational relations to their mental and nonmental surroundings (see Block, 1990).
Qualia in such bold senses have been rejected most forcefully by Dennett (1988). He describes several examples in which changes in whether we like or dislike certain tastes seem to change the tastes themselves, concluding that when someone 'thinks of "that taste" he thinks equivocally or vaguely' and 'need not try - or be able - to settle whether he is including any or all of his reactions' (1988, pp. 61-3). Nevertheless he accepts that, through the changes in likes and dislikes, 'the taste is (sort of) the same', and defenders of intrinsicality may hope to explain such taste similarities by appeal to reaction-independent components of experiences (see Lormand, 1994, for further defense of bold qualia).
An argument against the existence of intrinsic qualia can be built upon what G. E. Moore calls the 'diaphanousness' of perceptual experience:
Gilbert Harman argues as follows:
Defenders of intrinsicality may claim not to satisfy Harman's prediction; this response gains plausibility in cases of degraded perception (e.g., blurred or doubled vision), and it is not clear how Harman's argument is supposed to generalize from perceptual experiences to bodily-sensational, imaginative or thought experiences (for discussion of imagery by a philosopher in sympathy with Harman, see Tye, 1995). The prediction may hold for nondegraded perceptual experiences and perhaps 'upgraded' imaginings such as dreams, and in these cases perhaps it shows that no experienced features seem intrinsic to experience. One may hold that some experienced features are intrinsic to experience, but only by incurring a burden of explaining why these features seem to belong to trees and other nonmental objects. In fact, this burden remains even if qualia are taken to be relational features of perceptual experience, since the relevant experienced features are experienced as if they belong objectively to trees, and do not seem in experience to depend on the participation of the perceiver. Just as the eliminativist about phenomenal objects of experiences would do well to explain the illusory experience of their presence, so the noneliminativist about phenomenal properties of experience - whether intrinsic or relational - would do well to explain the illusory experience of their absence.
Here the discussion begins to shift from phenomenality to introspection. To clarify the apparent difference between phenomenal and introspective consciousness, consider whether a state can be conscious in one but not the other sense. Can there be nothing it is like to have a state, even when one is introspectively aware of it? Can there be something it is like to have a state, even when one is wholly unaware of it? The facts are murky and controversial, but it is important to be clear about the possibilities.
The introduction lists four kinds of states that are most clearly phenomenal: perceptual experiences, bodily-sensational experiences, imaginative experiences, and streams of thought. There are mental states not explicitly on this list, notably 'propositional attitudes' such as the belief that snow is white. Usually one's belief that snow is white is latent and unintrospected, though one can raise it to introspective consciousness easily. Normally there seems to be something it is like to have such an introspectively conscious belief (Goldman, 1993). However, there is another possibility to explore. What having the belief 'is like' may be completely accounted for by what it is like to have experiences accompanying the belief, such as auditory imaginings of asserting the words 'snow is white' (or 'I believe snow is white', or 'Mon Dieu! La neige! Blanche!'), or visual imaginings of some fictitious white expanse of snow, together with what William James (1890, pp. 287-8) describes as feelings or imaginings of moving eyeballs, eyelids, brow, breath, jaw-muscles, etc. as one thinks. Pending evidence of further aspects of what it is like to have the belief, this illustrates how there can be something it is like when one has an introspectively conscious state, although the state itself has no phenomenal character (Lormand, 1996; see Nelkin, 1989 for other reasons to posit nonphenomenal consciousness). Introspective consciousness - at least of the sorts available to beliefs - is unlikely simply to be phenomenal consciousness, and is unlikely simply to be sufficient for it.
Might introspection nevertheless be necessary for phenomenality? There is a tension between a 'yes' answer and the view that many species of animals can have experiences - that there is something it is like for cats and dogs to hurt or to see bright lights, for instance. It is implausible that these beings have Cartesian reflective knowledge that they hurt and see. This would require having concepts of hurting and of seeing, and perhaps a self-concept, and all this would seem to involve capacities beyond the reach of most nonhuman animals - for example, the ability to conceive of others as hurting and seeing, and the ability to remember or envision oneself hurting and seeing (see CONCEPTS). Notoriously, Descartes himself accepts that nonhuman animals are 'automata' without mental states of any sort. Defenders of a reflective-knowledge requirement may either mimic this strategy, denying that animals have conscious experiences (Carruthers, 1992), or else attempt to minimize the conceptual sophistication needed for the reflective knowledge (Rosenthal, 1990).
This tension is more commonly taken to be a serious strike against a reflective-knowledge requirement on phenomenality (e.g., McGinn, 1982, p. 52; Dretske, 1995, p. 18), especially given that a similar tension arises in the case of human infants. Thomas Reid objects against Locke that 'reflection ought to be distinguished from consciousness', since:
Even for beings with the requisite conceptual capacities, it seems implausible that reflective knowledge must accompany each of their experiences. At any given moment one can attend only to a small proportion of the sensory stimuli one encounters. It is also difficult to attend simultaneously to the outside world and to one's experience of it, as Auguste Comte argues: '[t]he thinking individual cannot cut himself in two - one of the parts reasoning, while the other is looking on' (1842, p. 21). Nevertheless, plausibly, there is something many inattentive perceptions of unattended stimuli are like; experience would be quite impoverished were it not for the contributions of background noises and odors, pressures on one's feet or seat, moisture under one's tongue, peripheral vision, and so on. It is possible to maintain that one continually forms reflective beliefs about these experiences, but this fits poorly with the difficulty of remembering these experiences (after they change, for example).
An introspective requirement on phenomenality can blunt much of the force of these objections by distinguishing inner perception from the formation of reflective beliefs, and by distinguishing inattentive introspection from attentive introspection. Just as one might sense a daffodil without having a concept of daffodils, or a tendency to remember the daffodil, so perhaps one can inwardly sense an experience without having a concept of experiences, or a tendency to remember the experience. Animals and babies might sense even if they cannot form beliefs; likewise, perhaps they can inwardly sense even if they cannot form reflective beliefs. Also, according to Locke, just as there can be passive sensation, so reflection need not be done intentionally or with attention (1689, p. 107; II, I, 7). Along these lines Brentano distinguishes between inner perception, which may be automatic and inattentive, and inner observation, which is actively guided by purposeful attention (1874, p. 29). It is true that a creature's most pressing cognitive needs require mental resources to be directed at the external world, but if inner perception is normally inattentive, it need not draw resources away from attentive outer perception. It is an open question whether there can be phenomenal experiences without any kind of introspective awareness of them, even of a primitive sort (but see section 7 below, and Dretske, 1993, for further objections).
Perhaps more thoroughly than Descartes (see section 1), Locke identifies the mental with the introspectively conscious, claiming that it is unintelligible 'that any thing thinks without being conscious of it, or perceiving, that it does so' because 'thinking consists in being conscious that one thinks' (1689, p. 115; II, I, 19). This completeness claim has been rejected by most subsequent philosophers, with the prominent exception of some in the broadly phenomenological tradition, following Franz Brentano (1874) and Edmund Husserl (1913) (see section 10).
The main evidence for introspectively unconscious mental processes is that they would fill certain theoretical gaps in the scientific explanation of behaviour and introspectible mental activity. This inferential strategy is most prominent in psychoanalytical attempts to explain otherwise bizarre dreams, associations among concepts, apparent slips of the tongue, emotional disorders, neurotic physiological reactions and so on (see FREUD, PSYCHOANALYSIS: DOCTRINES). Although the scientific status of such clinically-based explanations is controversial (see PSYCHOANALYSIS: CRITIQUES), alternative explanations are elusive; witness Jean-Paul Sartre's (1943) difficulties in trying to explain self-deception and 'bad faith' without appeal to unconscious mentation.
Furthermore, many replicable psychological experiments lead to parallel conclusions about introspectively unconscious mentation in more mundane settings. In one family of experiments (Lackner and Garrett, 1972), subjects are presented an ambiguous sentence in one ear, and disambiguating words in the other ear, but so quietly as not to be noticed consciously by the subjects - typically the stimulus is reported as a meaningless noise. Nevertheless, the subjects' interpretations of the ambiguous sentence are predictable from the meanings of the disambiguating words. This is evidence that subjects not only identify but understand the words, without introspective consciousness of doing so.
Similarly, there is evidence of vision without introspective consciousness of vision in cases of subliminal visual perception (Dixon, 1987) and 'blindsight' (Weiskrantz, 1988). In these cases subjects act on the basis of information about the visual features of objects, despite denying - sincerely and without hypochondria - that they have relevant visual experiences. Blindsight subjects have damage to certain neural pathways connecting portions of the retina to the visual cortex, yet in some sense they have perceptual states sensitive to these stimuli. For example, some ability to discriminate an 'X' from an 'O' is intact. This is evidenced by the preponderance of correct answers they can give to questions about the stimuli. When asked to reach for objects in blindsight regions, also, some subjects reflexively pre-orient their hand and fingers in ways suited to the specific shapes of the objects. What blindsight patients lack most clearly is any ability to introspect their perceptual states and abilities: they deny that they are perceiving; they respond to the stimuli only when coaxed to do so; and even then they take themselves merely to be guessing about what to say or do. Nevertheless, their guesses tend to be correct and their behaviours appropriate to the stimuli.
It is not only in unusual cases that there seem to be introspectively unconscious perceptual states. On virtually all detailed theories of normal vision, for example, cells in each retina register the amount of incoming light at various points, and cause further states representing sudden discontinuities of incoming brightness, which cause further representational states and, eventually, introspectively conscious visual experiences (see PERCEPTION). These early layers of visual processing seem well beyond the reach of introspection. Although these processes (unlike, say, blood flow in the brain) have many mentation-like features - they are assessable as correct or incorrect in relation to external stimuli, they may increase gradually in stability as evidence for them mounts, they may play a direct role in modulating intentional visuomotor action, etc. - they are at best somewhere in the vague boundary between the mental and the nonmental.
To the extent that introspectively unconscious perceptual states are phenomenal, they present a new threat to the claim that introspection is necessary for phenomenality (see section 6). Disagreement arises about whether cases of subliminal perception or blindsight involve phenomenal consciousness - perhaps blindseeing is like something, despite the subject's sincere denials; at any rate the cases are not clear enough to weigh decisively against the necessity claim.
There is more dispute about whether nonintrospectible information-bearing states in early visual processing are phenomenally conscious. On the view that they are, it would be difficult to explain why phenomenal visual experiences are not continually like double images, given that one has separate left-eye-caused and right-eye-caused early visual states. On behalf of the view, one possibility is that there is something it is like for one's early visual systems to have certain states, although there is nothing it is like for one to have them (for discussion of conscious subsystems, see White, 1987). Although this is a possibility, it seems no more likely than the possibility that there is something it is like for one's neurons when they fire.
Even if introspective consciousness is limited, it may be epistemologically interesting as an especially reliable means of access within its domain. Many philosophers have thought that introspective access to mental facts is more reliable than access to other empirical facts. Augustine writes in On the Trinity that 'nothing can be more present to the mind than the mind itself' (X, iii, 5), and asks rhetorically, 'what is so intimately known as the mind, which perceives that it itself exists and is that by which all other things are perceived?' (VIII, vi, 9; cf. Curley (1978:173)). Descartes devotes his Second Meditation to an argument that the mind is 'better known' than the body, and Locke also claims that our knowledge of 'Things without us' is 'not altogether so certain, as our intuitive Knowledge' (1689, p. 631; IV, XI, 3). As with completeness, most subsequent philosophers reject the infallibility of introspection, although many would agree that it is relatively reliable.
The claim of introspective infallibility is extremely bold. In other empirical domains, at best, certain mechanisms keep one's beliefs in rough accord with the facts (e.g., mechanisms of perception, reason and memory, and the persistence of facts when one is not continually checking them). But mechanisms fail; a mechanism of this complexity that could never possibly fail would be a miracle ('at least as mysterious as papal infallibility', says Dennett, 1988, p. 55). The same reason to expect fallibility holds for introspection: if there is the slightest mechanism correlating one's thoughts with one's thoughts about them, it should be breakable, and if there is no mechanism, a perfect correlation between the two would seem to be sheer luck.
Furthermore, scientific investigations of introspection have revealed widespread 'confabulation' in self-access. In identifying one's beliefs and motivations, one systematically but sincerely reports attitudes one thinks rational or statistically normal in the circumstances, even if one doesn't have them (see Nisbett and Wilson, 1977). For instance, in the 'bystander effect', increasing the number of joint witnesses to a needy person decreases the likelihood that any of them will assist. Bystanders rarely report this as a factor in their decision whether to help, however, often claiming instead to have reached a decision based solely on their own likelihood of success. According to Nisbett and Wilson, much allegedly 'introspective' access to attitudes consists of self-directed, fallible guesses, based at best on commonsense abilities to rationalize behaviour. Also, since these abilities are at work in one's access to others' mental states, this self-directed guesswork provides some reason to suppose, with Ryle (1949), that introspective consciousness is not interestingly more reliable than access to other minds.
In the face of this evidence the Cartesian may attempt to identify a restricted domain in which a kind of introspection is comparatively reliable (Ericsson and Simon, 1993) or even infallible (Dennett, 1969; Lormand, 1994). The model of rationalizing or statistical guesswork does not extend easily to introspection of phenomenally conscious experiences. For example, untutored subjects offer consistent and apparently reliable reports of stinging (rather than throbbing) pain 'feelings' when a limb has restricted blood flow. They seem not to infer these feelings in the way one might form beliefs about another's pain feelings, since no commonsense principles of rationality dictate that one should feel stinging rather than throbbing, and since the subject need know no relevant statistical information about how people feel in these circumstances.
Against any attempt to find a restricted domain safe for infallibility, Dennett argues that one can easily be wrong about the 'changes and constancies' in one's experience over even brief intervals of time (1988, p. 59). This weighs against infallible memory access to what it was like to have past experiences, though not against infallible or especially reliable access to ongoing experiences.
How should introspective consciousness be explained? While Lockean inner perception (see section 2) has some contemporary defenders, most notably David Armstrong (1980), this view has fallen on hard times in philosophy of mind.
How is inner perception supposed to be distinctively analogous to outer perception? Of course, inner perceptions are not generated by literal inner eyes, ears and their attendant experience-forming processes. Armstrong explains inner perception as being, like outer perception, 'selective' (incomplete), 'fallible' and 'causal'. This illuminates little, since probably all cognitive processes have these features, even one's most theoretical (versus perceptual) scientific beliefs, for example those about quantum-mechanics or cosmology. Another initially tempting idea is the Hindu one (see section 1) that inner perception is a causal but noninferential source of evidence about mental states (or, more cautiously, that it is as low as outer perception on flexible, all-things-considered inference). Might a mental state be introspectively conscious only if its bearer inwardly perceives the state, in this sense? One strong objection is that introspective access often involves self-directed theoretical inferences, often confabulatory ones (see section 8). It is therefore best to restrict inner-perception views to current phenomenal experience (in accordance with the suggestions at the end of section 8).
An influential objection is that inner perception requires phenomenal 'sense data' interposed between physical objects and one's perceptions of them (see SENSE DATA, PERCEPTION). Accepting inner perception may seem to involve accepting that one at best perceives outer objects indirectly through perceptions of phenomenal mental entities. But such a mediation theory would have difficulty explaining why inwardly perceiving sense data did not in turn require perceiving further entities ('sense-data data') and so on, infinitely. Such arguments against sense-data have been mounted against inner perception (as in Shoemaker, 1994), but with unclear effect. Inner perceptions needn't be interposed between objects and one's perceptions of them - the causal chain in perceiving a table needn't proceed from the table to an inner perception and then to a perception of the table. Rather, on a more natural view, the causal chain goes directly from the table to a perception of the table, and then (in cases in which the table-perception is introspectively conscious) to an inner perception of the perception of the table.
Dennett argues that inner perception of a 'Cartesian Theater' of consciousness would be too sharp to explain the vague conscious/unconscious distinction, and that inner perception is wasteful - 'once a discrimination has been made once [in outer perception], it does not have to be made again' (1991, p. 127). Yet it can be vague whether something is inwardly (or outwardly) perceived, and inner perception of an outer perception needn't re-represent features the outer perception is of, but instead may newly represent features of the outer perception (see Lormand, 1994, for further defense of inner theaters).
Perhaps the most influential objection to inner-perceptual introspection is based on Moore's 'diaphanousness' claim (see section 5). The objection is that, since each outer-perceptual modality (seeing, hearing, etc.) makes its own distinctive contribution to what experience is like, an additional modality of inner perception should be expected to make its own contribution, to change what it is like. But what it is like to introspect a perceptual experience seems simply borrowed from what it is like to have the experience itself (McGinn, 1982, p. 50-51). When one tries to attend to features of normal experiences, one normally 'sees through' the experiences to outer objects. So a fundamental disanalogy between outer perception and alleged inner 'perception' is that the former, but not the latter, has its own phenomenology or perceptual quality. This is evidence against inner perception of current phenomenal experiences.
On the other hand, if inner perception is necessary for phenomenality (see section 6), then instead of borrowing phenomenal qualities from an outer perception, as the diaphanousness objection alleges, inner perception helps generate these qualities together with the (otherwise phenomenally unconscious) outer perception. This may explain why inner perception doesn't add further qualia to an outer-perceptual experience; inner perception may already make its phenomenal contribution in the generation of an outer experience with qualia.
Two rivals to inner-perception accounts treat introspective access as epistemically less intimate than inner perception. First, James maintains that introspection is always retrospective (1890, pp. 187ff.), largely in reaction to Comte's denial that the mind can simultaneously split between ordinary thinking and awareness of that thinking (see section 6). James is unhappy with Brentano's response to Comte - that inattentive perception can be split between outer and inner domains - because James seeks to defend the reliance on careful, attentive introspective reports in experimental psychology. Second, some maintain that introspection is always laden with theoretical (versus perceptual) inferences. The experimental evidence for confabulation and expectation-driven inference (see section 8; cf. Lyons, 1986) suggests that introspection is often theory-laden and retrospective, but does not suggest that all cases of introspective consciousness are, including the seemingly noninferential consciousness of phenomenal experiences that seem to persist while being accessed.
One theory of consciousness that combines naturally with theory-ladenness is Rosenthal's (1990) 'higher-order thought' theory. (A thought or belief is 'higher-order' in virtue of being about mental entities rather than nonmental entities.) According to his view, a mental state is conscious just in case one forms, in a suitably direct way, a thought that one has the state. The state may generate its higher-order thought through inference so long as these inferences are not themselves conscious. This condition is intended to rule out cases in which one comes to think about a state through very indirect inference - say, solely through believing the testimony of a psychologist. On this view, even if introspective access to phenomenally conscious experiences is somehow inferential, it would seem noninferential simply because one lacks higher-order thoughts about the inferences.
At the other extreme from defenders of theory-ladenness and retrospection, many phenomenologists reject inner perception as not being intimate enough to explain introspective access. On one suggestion, some introspectively conscious mental states 'reflexively' represent themselves (in addition to representing other things). This conclusion is often embraced to avoid an infinite regress threatening the assumption that introspection is complete (see section 6): an experience represents itself rather than being represented by a separate introspective state which (assuming completeness) must in turn be represented by a separate introspection of the introspection, and so on. Brentano argues that '[t]he presentation which accompanies a mental act and refers to it is part of the object on which it is directed' (1874, p. 128). Husserl also suggests that '[i]n the case of a perception directed to something immanent [i.e., roughly, mental], ... perception and perceived form essentially an unmediated unity, that of a single concrete cogitatio' (1913, p. 112). And Sartre insists that 'the first consciousness of consciousness' - what he calls 'pre-reflective consciousness' - 'is one with the consciousness of which it is [a] consciousness' (1943, pp. 13-4). Given the prevalence of inferential, confabulatory access to one's mental states, reflexivity theories, like inner-perceptual ones, are best restricted to current phenomenally conscious experiences rather than to other mental states. Again, there is a possibility that one's only access even to these experiences is somehow much more confabulatory or inferentially sensitive to expectations than ordinary perception is, but pending evidence for this possibility the restriction to phenomenal experiences is reflexivity's best hope.
Since one often suffers ordinary perceptual illusions, the more analogous introspection is to perception, the more likely it would be that one would suffer naive introspective illusions about what one's conscious experiences are like. But it rarely if ever happens that one mistakes, say, a dull pain for a sharp pain, in the way that one mistakes a roadside cow for a horse. This may be evidence that introspection is sometimes neither inner perception nor self-directed theoretical inference, but a process with fewer breakable causal links. Some introspective access may be like one's psychologically primitive abilities to shift among mental states. Just as the transition from believing that p and q to believing that p presumably takes place without intermediate inference or inner perception, so might the transition from (say) believing that p to believing that I believe that p, or the transition from having a dull pain to believing that I have a dull pain. As Shoemaker proposes:
A challenge for this view is to explain lawful and systematic patterns among introspectible and nonintrospectible states, without an ad hoc assumption, for each pattern, that it happens to be 'wired' to higher-order beliefs in the right way. For example, why aren't brain states governing autonomic bodily functions introspectible? Why are perceptual experiences introspectible but not subliminal perceptions and early perceptual states? Why does it seem easier to introspect one's fleeting thoughts than one's deeply held beliefs?
All of the theories described thus far in this section reject the etymological suggestion that 'introspection' is a kind of inner perception, while retaining the assumption that a subject's introspective 'access' to a mental state is always a matter of somehow representing the state. Further alternatives emphasize other forms of access to a state, or the state's functional relations to processes other than a subject's awareness of them. Verbal reportability is the process most frequently appealed to as an alternative requirement for introspective consciousness (Dennett, 1969, 1978), in keeping with ordinary and scientific reliance on reportability as a symptom of consciousness. One threat is that reportability may only seem relevant to consciousness because it correlates somewhat with inner-directed representation. Normally in reporting one perceives one's reporting - hears one's speech, feels one's facial motions, etc. - and is thereby in a position to understand one's reports - to recognize one's own voice and realize which mental states one's words express. By contrast, if there is speech without any kind of self-perception, perhaps as in some forms of hypnosis or sleeptalking, this may not seem sufficient for, or even relevant to, introspective consciousness.
Dennett's construct is nearer to Block's (1993) notion of 'access consciousness', as distinguished from introspection and from phenomenality. In Block's terms, a mental state is access conscious if it is poised for free rational control of inference and action. The relevant actions may, but need not, include verbal actions, and the relevant inferences may, but need not, include Cartesian reflective knowledge. Although access consciousness has played little role in the history of philosophical discussions of consciousness, many contemporary philosophers and scientists employ comparable notions in attempts to explain consciousness generally (Baars, 1988; Dennett, 1991; Tye, 1995; Chalmers, 1996; cf. Kirk's 'direct availability' in section 3).
References and further reading
*Aquinas, T. (1273) Philosophical Texts, trans. 1951 by T. Gilby, New York: Oxford University Press. (Classic synthesis of Christianity and Aristotelianism; posits an inner-directed 'common sense' - see section 1.)
*Aristotle (1968) De Anima Books II, III, trans. by D. Hamlyn, Oxford: Clarendon Press. (Maintains that we see that we see - see section 1.)
*Armstrong, D. (1980) 'What is consciousness?', in The Nature of Mind, Ithaca: Cornell University Press, 55-67. (A sketch of an inner-perception view - see section 9.)
*Baars, B. (1988) A Cognitive Theory of Consciousness, Cambridge, Cambridge University Press. (A cognitive psychologist tries to explain consciousness as a 'global workspace' - see section 10.)
*Block, N. (1980) 'Are absent qualia impossible?', Philosophical Review, 89, 257-74. (Answers 'no', in response to Shoemaker, 1984, ch. 9. Clear but increasingly intricate as possible replies mount.)
*------ (1983) 'Mental pictures and cognitive science', in Philosophical Review 92, pp. 499-541. (Philosophical account of mental imagery research - see section 5.)
*------ (1990) 'Inverted Earth', in Tomberlin, 1990, 53-79. (The inverted qualia argument mentioned in section 5 is a sidelight to a novel argument against functionalism.)
*Brentano, F. (1874) Psychology from an Empirical Standpoint, trans. 1973 by A. Rancurello et al., London: Routledge and Kegan Paul. (Study of intentionality and reflexive consciousness - see section 10.)
*Carruthers, P. (1992) The Animals Issue, Cambridge: Cambridge University Press. (Uses a higher-order-thought theory of consciousness to argue that nonhuman animals lack phenomenal experience - see section 6.)
*Chalmers, D. (1996) The Conscious Mind, Oxford: Oxford University Press. (Appeals to subjectivity in a defense of dualism, epiphenomenalism, and panpsychism about phenomenal consciousness - see sections 3-4.)
*Curley, E. (1978) Descartes Against the Skeptics, Cambridge: Harvard University Press. (Criticizes Ryle's 1949 reading of Descartes as an introspective infallibilist - see section 1. Notes sympathetically that Descartes cannot simply be accused of a 'foolish consistency' on the issue of introspective completeness.)
Davies, M. and G. Humphreys, eds (1993) Consciousness, Oxford: Blackwell. (A balanced group of first-rate philosophical and psychological essays. The introduction would make a good follow-up to this entry, and the bibliography is extensive.)
*Dennett, D. (1969) Content and Consciousness, London: Routledge and Kegan Paul. (In the closing chapters, emphasizes a connection between consciousness and language use - see section 10; thereby defends infallibility of verbal reports on conscious states - see section 8.)
*------ (1978) 'Toward a cognitive theory of consciousness', in Brainstorms, Cambridge: MIT Press. (Characterizes conscious states as those available for linguistic report - see section 10.)
*------ (1991) Consciousness Explained, Boston: Little, Brown. (An attack on introspective theories of phenomenal consciousness, with some leanings towards eliminativism - see section 10.)
*Dretske, F. (1993) 'Conscious experience', Mind. (Argues that one can be aware of x without being aware that x is F, for any F - see section 6.)
*------ (1995) Naturalizing the Mind, Cambridge: MIT Press. (An attempt to explain consciousness in terms of 'information functions'; criticizes introspective theories of phenomenality - see section 6.)
*Descartes, R. (1637, 1641, 1648) The Philosophical Writings of Descartes, vols I-III, trans 1985, 1991 by J. Cottingham et al., Cambridge: Cambridge University Press. (The boldest epistemological claims for introspection are in the Fourth Replies - see sections 1, 6-8. Note: I have used 'conscious' in place of the translator's 'aware' to render Descartes's Latin 'conscius' and French 'connaissant' and 'conscient'.)
*Dixon, N. (1987) 'Subliminal perception' in R. Gregory, ed. The Oxford Companion to the Mind, Oxford: Oxford University Press, pp. 752-755. (Brief overview of the research and controversies - see section 6.)
*Ericcson, K. and H. Simon (1993) Protocol Analysis, Cambridge: MIT Press. (A scientific defense of introspective reliability against Nisbett and Wilson, 1977, and others - see section 8.)
*Flanagan, O. (1992) Consciousness Reconsidered, Cambridge: MIT Press. (A good extended introduction to the central philosophical issues. Responds to McGinn, 1991 - see section 3.)
*Harman, G. (1990) 'The intrinsic quality of experience', in Tomberlin, 1990, pp. 31-52. (Argues against intrinsic qualia using diaphanousness and the rejection of sense data - see section 5.)
*Husserl, E. (1913) Ideas, trans. 1962 by W. Gibson, New York: Macmillan. (The classic work of phenomenology as a reflexive study of consciousness - see section 10.)
*Jackson, F. (1982) 'Epiphenomenal qualia', Philosophical Quarterly, 32, 127-36. (Contains the 'knowledge argument' against physicalism - see section 3 - and a defense of epiphenomenalism - see section 4.)
*------ (1993) 'Armchair metaphysics', in J. O'Leary-Hawthorne and M. Michael, eds., Philosophy in Mind, Dordrecht: Kluwer. (Perhaps the clearest presentation of the explanatory gap argument against physicalism - see section 3.)
*James, W. (1890) The Principles of Psychology, reprinted 1993 Cambridge: Harvard University Press. (Packed with sensitive but reasonably cautious reports from the heyday of introspective psychology - see section 6. Defends introspection as retrospection - see section 10.)
*Kant, I. (1787) Critique of Pure Reason, trans. 1968 by N. K. Smith, London: Macmillan. (Classic synthesis of empiricism and rationalism; defends inner sense - see section 2.)
*Lackner, J. and M. Garrett (1972) 'Resolving ambiguity: effects of biasing context in the unattended ear', Cognition 1, pp. 359-72. (Psycholinguistic experimental paradigm with implications for subliminal perception - see section 6.)
*Leibniz, G. (1714) 'The Principles of Nature and Grace, based on Reason', in L. Loemker, ed., Philosophical Papers and Letters, 1969, Dordrecht: D. Reidel, pp. 636-42. (A brief, popular introduction to Leibniz's metaphysics; defends apperception - see section 2.)
*Levine, J. (1993) 'On leaving out what it's like' in Davies and Humphreys, 1993, 121-36. (Careful statement of the 'explanatory gap' argument; emphasizes epistemological rather than metaphysical conclusions - see section 3.)
Lewis, C. S. (1960) Studies in Words, reprinted 1990 Cambridge: Cambridge University Press. (Literate history of 'conscious' and other philosophically important terms.)
*Locke, J. (1689) An Essay concerning Human Understanding, P. Nidditch, ed., 1975, Oxford: Oxford University Press. (Classic work of empiricism; treats consciousness as complete and infallible 'reflection' - see sections 2, 6-8.)
*Lormand, E. (1994) 'Qualia! (now showing at a theater near you)', Philosophical Topics. (A defense of qualia and introspective theories of phenomenal consciousness against Dennett, 1988, 1991 - see sections 5, 8-9. With other commentators on Dennett and Dennett's replies.)
*Lycan, W. (1990) 'What is the subjectivity of the mental?', in Tomberlin, 1990, 109-30. (A friend of inner perception treats subjectivity - see section 3.)
*Lyons, W. (1986) The Disappearance of Introspection, Cambridge: MIT Press. (A valuable historical survey of theories of introspection, and a defense of theory-ladenness - see section 10.)
Marcel, A. and E. Bisiatch, eds (1988) Consciousness in Contemporary Science, Oxford: Oxford University Press. (Equal time given to essays by philosophers, neuroscientists and cognitive psychologists.)
*McGinn, C. (1982) The Character of Mind, Oxford: Oxford University Press. (A brief but rich introduction to philosophy of mind; criticizes inner sense - see section 6.)
*------ (1991) The Problem of Consciousness, Oxford: Blackwell. (Denies that human beings can ever grasp how consciousness is physical, even if it is - see section 3.)
Metzinger, T., ed. (1995) Conscious Experience, Thorverton, UK: Imprint Academic. (Large collection of philosophical essays, with an extensive bibliography.)
*Nagel, T. (1974) 'What is it like to be a bat?', reprinted 1979 in Mortal Questions, Cambridge: Cambridge University Press, 165-180. (Made the 'what it is like' idiom and subjectivity arguments popular in philosophical discussions of qualia - see sections 2, 3.)
*------ (1979) 'Panpsychism', in Mortal Questions, Cambridge: Cambridge University Press, 181-195. (Uneasy defense of panpsychism against emergentism and reductionism - see section 4.)
*Nelkin, N. (1989) 'Propositional attitudes and consciousness', Philosophy and Phenomenological Research, 49, 413-30. (Argues for the nonphenomenality of conscious attitudes - see section 6.)
*Nisbett, R. and T. Wilson (1977), 'Telling more than we can know: verbal reports on mental processes', Psychological Review, 84, 231-59. (Influential psychological case for confabulatory and expectation-driven access to attitudes - see section 8.)
*Plato (1961) Collected Dialogues, E. Hamilton and H. Cairns, eds., Princeton: Princeton University Press. (Uses the slave-boy argument in Meno to argue that learning is recollection of knowledge from previous lives - see section 1.)
*Putnam, H. (1963) 'Brains and behavior', reprinted 1975 in Mind, Language and Reality, Cambridge: Cambridge University Press, 325-341. (Argues against logical behaviourism - see section 4.)
*Radhakrishnan, S. and C. Moore (1957) A Source Book in Indian Philosophy, Princeton: Princeton University Press. (Contains ancient references to inner perception among both defenders of Hindu tradition and skeptics - see section 1.)
*Raffman, D. (1995) 'On the persistence of phenomenology', in Metzinger, 1995. (Argues that the physicalist cannot use demonstrative or descriptive introspection to explain subjectivity - see section 3.)
*Reid, T. (1785) Essays on the Intellectual Powers of Man, reprinted 1969, Cambridge: MIT Press. (An attempt to inject 'common sense' into empiricism; emphasizes existence of preattentive consciousness - see section 6.)
*Rey, G. (1986) 'A question about consciousness', in H. Otto and J. Tuedio, eds, Perspectives on Mind, Dordrecht: D. Reidel, 5-24. (Argues that our concept of consciousness is oversimple and incoherent; uses first-person knowledge against spiritual and biological accounts - see section 4.)
*----- (1997) Contemporary Philosophy of Mind: A Contentiously Classical Approach, Oxford: Blackwell. (Chapter 11 provides a relatively detailed functionalist theory of some phenomenal states, and attempts to explain mistaken 'reification' of mental images - see section 5.)
*Rosenthal, D. (1990) 'A theory of consciousness', ZIF Report 40, Bielefeld: Center for Interdisciplinary Research. (A higher-order-thought theory - see section 10.)
*Ryle, G. (1949) The Concept of Mind, London: Hutchinson. (Attack on Descartes's dualism and epistemological claims, and defense of philosophical behaviorism - see section 8.)
*Sartre, J. (1940) The Psychology of Imagination, trans. anon. 1948, New York: Philosophical Library. (Sustained attack on the illusion of immanence - see section 5.)
*------ (1943) Being and Nothingness, trans. 1956 by H. Barnes, New York: Philosophical Library. (Classic work of existential phenomenology; defends 'pre-reflexive consciousness' - see section 10.)
*Shoemaker, S. (1984) Identity, Cause, and Mind, Cambridge: Cambridge University Press. (Ch. 9, 'Functionalism and qualia' is an intricate defense of functionalism against zombies - see section 4. Ch. 14, 'Absent qualia are impossible' is an intricate reply to Block, 1980.)
*------ (1994) 'Self-knowledge and "inner sense"', Philosophy and Phenomenological Research, 54, 249-314. (An extended attack on inner perception - see section 9.)
*Smart, J. (1959) 'Sensations and brain processes', Philosophical Review, 68, 141-56. (Defense of materialism against phenomenal-object and other objections - see section 5.)
*Smart, N. (1964) Doctrine and Argument in Indian Philosophy, London: George Allen and Unwin. (Describes the Hindu doctrine of an inner-directed 'mind-organ' - see section 1.)
*Tomberlin, J., ed. (1990) Philosophical Perspectives, vol. 4, Atascadero, CA: Ridgeview. (Several interesting philosophical papers on consciousness and action.)
*Tye, M. (1995) Ten Problems of Consciousness, Cambridge: MIT Press. (An attempt to explain phenomenality in terms of intentional content that is 'poised' for cognitive influence - see section 10; appeals to demonstrative introspection against subjectivity arguments - see section 3; appeals to diaphanousness against intrinsic qualia - see section 5.)
*van Gulick, R. (1993) 'Understanding the phenomenal mind: are we all just armadillos?' in Davies and Humphreys (1993), 137-54. (Reviews responses to subjectivity arguments about qualia - see section 3.)
*Weiskrantz, L. (1988) 'Some contributions of neuropsychology of vision and memory to the problem of consciousness' in Marcel and Bisiatch, 1988, 183-99. (Brief, directed discussion from the leading authority on blindsight - see section 6.)
*White, S. (1987) 'What is it like to be an homunculus?', Pacific Philosophical Quarterly, 68, 148-174. (Thought experiments relevant to conscious subsystems - see section 6.)
*Whyte, L. (1962) The Unconscious Before Freud, London: Tavistock. (A compendium of premodern and early modern views of 'hidden' behavioural influences - see section 1. Citations are lax.)