In essence, emergence is said to supervene on lower-level foundational components of a system, thus rendering the emergent properties non-reducible to the properties (including the laws manifest by) those foundational components.
That emergence actual exists, as a mater of fact and not just as an intellectual nominalist possibility, can be clearly shown in many biological systems. One important example is that of the reflex arc, the set of receptors, receptor (afferent) neurons, joined linearly with a corresponding set of effectors, effector (efferent) neurons, yielding a causal end-to-end stimulus-response phenomenon that is fully accounted for interns of these neuro-motor elements. Yet, the reflex-arc does not normally manifest itself in the normal neurally integrated whole of the living organism’s nervous system. Here we see the very same neurons (fully isolable as elements of their corresponding reflex circuit) being overridden (supervened) by higher-level, central controlling mechanisms, that enable subtle intricate orchestration of effectors in response to centralized integration and processing of multiple afferent patterns of stimulation. This is the main theme of Sir Charles Sherrington’s seminal work ‘The Integrative Action of the Nervous System.’
So higher-level processes and structures can emerge from, or rather be layered upon, more primitive processes and structures. This is the law of hierarchical development of living organisms and their associated processes. But we cannot know, necessarily in every case how this layering (which I will call emergence) takes place. We cannot necessary know the detailed mechanisms and processes involved nearly so well as we can come to know the resulting systems, their properties and their laws.
What we cannot and must not do, however, is to allow science to set the standards for philosophy, especially for ontology. Rather it must be the other way round: ontology teaches us what kinds of principles of being and what categories of lawfulness can exist for a given class of substances. This is of course, Aristotelian.
The Explanatory Gap
Joseph Levine is generally credited with the invention of the term ‘explanatory gap’ to describe our ignorance about the relationship between consciousness and the physical structures which sustain it. Levine’s account of the problem of the explanatory gap in his book Purple Haze (2001) may be summarized in terms of three theses, which I will describe and name as follows:
(SP) Supervenience physicalism: every minimal physical duplicate of the actual world is a duplicate in every respect.
(DE) Deductive explanation: the explanation of consciousness must consist in a deduction of the truths about consciousness from the physical truths.
(EG) Explanatory gap: we lack an adequate deductive explanation of all the truths about consciousness in physical terms.
SP, DE and EG are not inconsistent, since consciousness could supervene on the physical without its being explicable. Consciousness might be wholly determined by the physical but nonetheless be inexplicable. This is what ‘mysterians’ believe. Nonetheless, Levine thinks (and many agree with him) that there is a challenge here which physicalism has to meet. If physicalism is to be an adequate account of the world, it must not postulate too many ‘brute’ or inexplicable correlations and identities. Accepting a mere brute correlation is accepting a mystery. In this he is echoing Thomas Nagel, who said famously that someone who asserts that consciousness is a process in the brain would be in the same epistemological position as an ancient Greek who asserted that matter is energy: they would have said something true, but they would not have understood how it could be true (Nagel 1974).
– from Cosmic Hermeneutics vs. Emergence: The Challenge of the Explanatory Gap by Tim Crane
4. To this extent the form is at the same time a final cause for the potentialities which are present in order to make its emergence possible. This can justify, then, Aristotle’s description in Physics 1.9 of form as an object of striving and matter as the entity which in so far as it is matter strives after form. – Notes to Aristotle’s Natural Philosophy in Stanford Encyclopedia of Philosophy
* Do not cite or quote this page. It is under development and its contents are tentative. – bioperipatetic