In the late 1970s, Benjamin Libet showed that motor cortex activity preparing for an action occurs before the conscious act of willing that action. (Here is a nice demonstration of the experiment by Patrick Haggard.)
Libet's result has been replicated countless times (as above), and though it is perhaps rash to generalize too broadly, let's just say we have strong evidence for:
- Conscious acts of "willing" an action occur after the brain activity that cause the action, and so
- Conscious acts of willing do not cause action.
As a philosopher, which of the following conclusions can I legitimately draw?
A. Free will is an illusion.
B. Since free will is real, action is determined by both motor cortex activity and conscious acts of willing. (2 is therefore mistaken.)
C. Since free will is real, actions may be free even when they are not caused by conscious acts of willing.
D. Since free will is real, so-called "conscious acts of willing" are awareness of will, not will itself.
Note that B and D are causal theses (D because it implicitly posits a causal connection between cortical activity and the "acts of willing"). The question is whether philosophers can legitimately draw such conclusions from philosophical intuitions such as the reality of free will. Shouldn't causal theses be based purely on empirical fact? Or can a philosophical thesis + empirical fact yield a causal connection that isn't implied by the empirical fact alone?
One way to respond to this query is to insist that the reality of free will is empirical—it is an observed causal connection between certain conscious acts and action. So philosophy does have a special empirical basis, namely introspection. But if this is right, then the proposition should be undercut by Libet's evidence to the contrary. In other words, if introspection yields empirical facts, then it must be in competition with other sources of empirical facts. But B and D are (to somewhat different degrees) based on an unwillingness to compromise on the supposed observation of a causal connection between willing and acting. To put this another way: the super-high evidential status claimed for introspection belies its empirical content.
The broad issue of philosophy's empirical entanglement is relevant because of two quite bold suggestions that we have seen lately. One of these is from Tom Nagel. Nagel starts from an empirical assertion, namely that there is insufficient genetic variation to generate consciousness by natural selection. (How he knows this, I have no idea.) So, he says, natural selection doesn't make consciousness probable before the fact—at best it offers an explanation ex post facto. (He doesn't seem to be aware that many biologists and philosophers have marked this as a feature of explanations by natural selection quite generally. Nothing special about consciousness: the emergence of bipedalism isn't before-the-fact probable either.)
From these shaky premises, Nagel infers that the Theory of Natural Selection doesn't make the emergence of consciousness intelligible. So far he is in secure philosophical territory. Bad philosophy perhaps, but it is philosophy.
And now comes the causally loaded conclusion: to ensure intelligibility, there must be teleologically loaded processes that direct mutation (or something of that sort). Here we have a classic example of what I am querying. A philosophical thesis about intelligibility leads to a substantive causal thesis. Call it pure speculation, and I have no problem. OK, I lied. I do have a problem: why must the world be intelligible? Are we justified in positing extra causes just to ensure intelligibility? Putting this aside, however: can we call Nagel's train of thought philosophical analysis?
Another example, as I argued in an earlier post, is Russell's postulation of neutral monism, which has drawn some sympathy from David Chalmers. Consciousness is not materially determined. So we should entertain the hypothesis that matter and mind might both be modifications of some other fundamental type of substance? Or perhaps that phenomenality is a fundamental property of matter. Again: pure philosophical analysis leading to a substantive causal hypothesis.
Given intuitions such the ones that Chalmers and Nagel express, there are three ways to go.
I. One can say: If, as some think, there is insufficient genetic variation to generate consciousness, one might want to entertain the creative mutation hypothesis. Personally, I think that both the antecedent and the inference are weak. But at least it precludes rubbish subtitles like "Why the neoDarwinian materialist picture is almost certainly false."
II. One can, provided one is well acquainted with the science, advance scientific hypotheses such as Fodor's syntactic theory of mind. Perhaps this is how we should interpret D above. I am fond of this alternative, though it is very high risk. The much-missed Denis Dutton advanced sexual selection as an explanation of "the art instinct" and I am just about to offer an individual selection example (in a paper in Antwerp).
III. One can attempt to evaluate whether a sequence of events is or is not causally connected. Wes Salmon argued that the movement of a spot of light is not causally connected in the way that the movement of a struck tennis ball is. But he did this on the basis of philosophical analysis of a physical account of the movement of the spot of light. Similarly, I have argued (alongside André Ariew, Denis Walsh, and Tim Lewens) that natural selection is similarly not a causally connected process. Our co-blogger, Roberta Millstein vehemently opposes this thesis. (See here for a personal account of the argument.) These are instances of what philosophers do best—evaluate.
So when can a posteriori propositions about factual matters be asserted on purely philosophical grounds? There are cases, but they have to be treated with a lot of caution.