Lamar H. recently left a comment on my post entitled "Determinism is Skepticism, so what about Eliminativism?" I didn't notice the comment until today because that post is quite old, and I don't have Lamar's e-mail, but he asked for a response and his comment is good quality philosophy, so I'll post this and hope he sees it; he generates some good discussion here during the otherwise hectic last week of class.
My original post floated this idea: if we define a philosophically skeptical argument as any argument that purports to show that I don't know something that I am certain that I do know, then the claim of the hard determinist, that for any action I take I could not have acted otherwise, looks like a philosophically skeptical argument. If this is true, then any arguments that I have that seem to be effective counters to skepticism ought to be deployable against determinism (the further point in the original post about eliminativism does not enter in here). I won't reproduce Lamar's whole comment here, but you can read it by scrolling down to the post (or click on the December 2006 file). I'll quote from it: "(T)he claim that nothing can be known for sure and the claim that a particular thing we'd like to think we know for sure (viz., that we have control over our actions) is not true, are two different claims. One is an epistemological claim concerning the limits of human knowledge while the other is a metaphysical claim concerning the ontology of human behavior." Lamar takes the definitive point here to be, I think, that the determinist claims to know something (to have a positive argument), not to doubt that knowledge is possible, and thus determinism is "a precisely non-skeptical claim." I think that Lamar is right that the determinist is not making a skeptical argument. I take Lamar's point that the positive arguments for hard determinism are metaphysical and not epistemological: physicalism about persons plus causal determinism yield hard determinism. The determinist claims that accepting these premises entails hard determinism, and thus makes a knowledge claim, and thus is no kind of skeptic. Nonetheless I am still persuaded that the kinds of arguments that Wittgenstein makes against skepticism can indeed be deployed against the hard determinist (and, although this is a shakier claim, I still suspect that Hume, properly interpreted, aims at a Wittgenstein-like position that these are pseudoproblems. I don't think that Hume takes either skepticism or determinism seriously, although he cheerfully concedes to the impossibility of disproving them).
Lamar, if I get him right, is more interested in determinism than he is in skepticism (not that that matters to the argument), but I want to raise some questions about whether his characterization of skepticism is a) sound and b) distinct from mine. Lamar characterizes skepticism as the view that knowledge is impossible, while I characterize philosophically skeptical arguments as those that purport to show that I don't know something that I am certain that I do know. I will call Lamar's version "global skepticism" (sometimes "global skepticism" is used to denote the view that my senses might be entirely misrepresenting the world to me, or the view that the external world might not exist; here I mean the view that knowledge is impossible).
First of all note that the varieties of skepticism familiar from Descartes' Meditations tend to take the form that I suggest: I think that I know that I'm not dreaming, I think that I know that other minds exist, I think that I know that causal laws will remain in effect in the future, but, the skeptic says, I don't really know these things. I don't know, notably, that my senses are representing the world to me as it "really" is (and this worry depends on a representational theory of mind). But the global version propounded by Lamar (knowledge is not possible) is not like these Cartesian versions. There is no coherent sense of the meaning of the verb "to know" that can sustain global skepticism. If you don't mean to refer to some specific possibility - my senses may be deceiving me, other people may be zombies, I may be dreaming, etc. - then it is not possible to make sense of the claim.
The incoherence of this global version of skepticism is also apparent (the same problem with this characterization is apparent) when we consider the self-refuting character of the claim: that the global skeptic claims to know that knowledge is impossible. There is a trivial sense in which global skepticism militates against any claim whatsoever, including any claim that I am free, or any claim that I am determined, but that just shows, again, that global skepticism is philosophically uninteresting, since it can make no meaningful claim.
This kind of Wittgensteinian (and, I think, Humean) argument about meaning (and the limits of language) also yields (I still think) an argument against hard determinism. The argument, that is, is that hard determinism is incoherent, notwithstanding Lamar's (correct, I think) point that the hard determinist has a positive argument that he takes to demonstrate the necessary truth of hard determinism, rather than an epistemological worry that I can't prove that I act freely. Wittgenstein argues that I neither believe nor disbelieve that the external world exists; the "external world" is part of the ground (as Paul Tillich might say) of belief. Freedom, I am suggesting, is like that: it is not a proper object of belief or disbelief, I can no more choose to "believe" it than I can choose to "disbelieve" it. Notice that this argument overcomes Holbach's argument that a "phenomenological" defense of freedom fails because the experience of freedom could just be an illusion itself caused by the causal antecedents. The response to the hard determinist is: what you are saying does not mean anything, it does not perform (it cannot perform) any communicative function. But that is precisely the argument against skepticism about the senses, about the external world, about other minds, etc. Lamar?