I’m considering the implications of causal determinism on our cognitive faculties. I’m trying out an argument here that probably looks familiar, being more or less a hodgepodge of some other arguments.
1. The probability of your reasoning processes being correct on any given belief, given determinism, is inscrutable.
2. Either your beliefs can be regarded to come from a reliable source or they cannot.
3. If they can, then any non-circular form of reasoning to support this can be used for libertarian free will (LFW) as well.
4. If that form of reasoning can be used for LFW, then LFW has the explanatory advantage as an account of the will.
5. If your beliefs cannot be regarded to come from a reliable source, then no one belief has any reason to be held as true over any others.
6. If no one belief has any reason to be held as true over any others, then the belief that you are causally determined has no reason to be held as true.
7. Therefore, either LFW has the explanatory advantage as an account of the will, or the belief that you are causally determined has no reason to be held as true.
1 is just saying that, given causal determinism about your cognitive faculties, we can ask ourselves the question: What is the probability that my reasoning processes that are supposed to confer justification on my beliefs are correct? The answer seems to be that such a probability is inscrutable. Why? Because for any way you would go about assessing that probability, you would be appealing to your cognitive faculties and reasoning processes. But how do you know that these reasoning processes are correct, given causal determinism about them? Suppose that an evil demon is just pulling levers to give you occurrent beliefs and reasoning processes. Of course it would seem to you to be correct; it’s not as though the demon was causing only some beliefs, leaving your reasoning process and general cognitive faculties untouched. No, all of your noetic structure is determined, on this supposition.
Now notice what I’m not doing here. I’m not saying something like “your cognitive faculties are unreliable” or “you cannot know if any of your beliefs are correct.” I am saying “your cognitive faculties are unreliable, given determinism,” and you cannot know if any of your beliefs are correct, given determinism.” These are epistemological concerns. Now whether (1) can be ultimately rejected by the determinist will pop up in a later premise. For now, let’s move to (2). That premise is a disjunction that exhausts all of the logical possibilities. It occurs to me that most determinists will likely want to affirm the first disjunct of (2). That leads us to (3). Whatever non-circular rescue that can be used can also be used to support LFW. Where do I get that? Well, think of the type of things a determinist might want to use: the idea of logical laws. Though attempting to fully justify logical laws is circular on LFW also (since one must presuppose logic in order to use it), it’s just as bad or worse on determinism, since the determinist must hold that even considering the laws contains a causally determining influence, one not present were LFW to be true. What about God’s ensuring it to be the case that one’s reasoning process is reliable. Well, that contains two major issues. First, if God is causally determining everything, it at least appears as though God does not uniformly make it the case that everyone’s reasoning process is reliable; how do you know yours is not similarly affected? That leads to the second major issue: appealing to what God would do (or even has done) assumes a kind of reliability to belief. That’s fine and good, since (3) entails a rejection of (1), but let’s see if this option is available to the libertarian: yes it is!
(4) is just the claim that since all of the same solutions are available to those of us who believe in LFW, then LFW has the explanatory advantage. Why? Simply because it seems to us that we have LFW. All things being equal, simplicity is a preferable criterion in adjudicating between different explanations. And the simplest explanation of our seeming to have LFW is, on this discussion, actually having LFW.
So what happens if you bite the bullet, and accept that your beliefs cannot be regarded to come from a reliable source with respect to your cognitive faculties? Well then it follows that none of your beliefs can be espoused with any degree of confidence, and if that happens, then the belief that your cognitive processes are causally determined cannot be espoused with any degree of confidence.
Thus, no matter which way you go, either LFW has the explanatory advantage as an account of the will, or the belief that you are causally determined has no reason to be held as true. If the former, then you should give up causal determinism and embrace LFW. If the latter then at the weakest you should be agnostic about the will. But it’s even worse than this for the causal determinist: for surely you now believe something about the preceding argument and any of the premises. So you must affirm that there is a belief such that it can be held with confidence. But then, by modus tollens, you ultimately commit yourself to leaning LFW. I’m sure there are both worries about the argument’s premises and responses to things I have claimed. I’d like to hear them!
 Note well, on this argument, it only needs to be just as bad, not worse (though obviously that would be an added bonus).
 Simplicity also seems to be a properly basic belief.