There are various forms of skepticism, and they tend to come in local and global varieties. A local form of skepticism could be skepticism about intuitions that favor deontological moral judgments, which is endorsed by Peter Singer, among others. Global skepticism could be about all assertions about the external world (besides assertions about our epistemic relations to it or lack thereof). In this post, I will explore global skepticism about reasons.
Reasons, broadly construed, are just things that count in favor of some course of action or other. The fact that taking Advil will relieve my headache is a reason to take the Advil, because that fact counts in favor of the course of action of taking the medication. The fact that my new colleague told me her name is Erika is a reason for me to believe that her name is Erika, because that fact counts in favor of forming that belief. The fact that calling a friend a slur will hurt your friend is a reason to refrain from calling them a slur, etc. The ‘counting in favor of’ relation is most likely primitive. Any attempt to pull the concept apart into constituent parts leads back into a cluster of inter-defined concepts, such as ‘reason’.
Global skepticism about reasons (GSR) is the thesis that either there are no reasons (nihilism) or nobody is justified in considering anything to be a reason for some course of action. The differences between the disjuncts are immaterial to the point of this post, so I will just use “GSR” to refer to the disjunction rather than either disjunct in particular.
The reasons skeptic presents the non-skeptical realist about reasons with a challenge, as does any skeptic about any domain of alleged knowledge. The skeptic will present a far-fetched scenario in which a subject has access to the same evidence she has in the actual world, yet the subject is massively deceived in some way. The skeptic will then require the realist to provide ways of ruling out that scenario, otherwise the realist cannot demonstrate that she is not in that scenario herself (anti-skeptics have also attempted to show that the form of the skeptic’s challenge is somehow incoherent, or self defeating in some way). The general argument is topic neutral, and probably can be applied to any body of alleged knowledge.
When it comes to GSR, however, there is a problem. The skeptic about reasons is presenting the realist about reasons with a challenge, thus inviting her to enter into a dialectic. Entering into a dialectic is entering into a reason-giving situation; the skeptic will present her reasons for thinking skepticism is true, and the realist will present her reasons for thinking skepticism is false, then the skeptic will reply to the realist, and the realist will reply to the skeptic, etc. The issue should have become apparent already; the skeptic is claiming to have reasons to believe that we are not in a position to know that we have any reasons for anything (or there are no reasons at all). This is akin to providing an a priori argument against a priori justification/knowledge. What the skeptic is doing is engaging in a self-defeating intellectual enterprise, since she is attempting to provide reasons to think that we have no reason to believe in reasons.
The upshot of all of this is that one cannot provide a skeptical argument against reasons in general, since the entire enterprise presupposes that we have at least some reasons to believe some things. Global skepticism about reasons is necessarily self-defeating, due to the structure of skeptical challenges and the nature of dialectics. At best, one can provide skeptical arguments for reasons about certain things, such as reasons to be moral, or reasons to believe that induction is a reliable way of obtaining knowledge. But one cannot provide a skeptical argument against reasons as such. Denying that we have any reasons at all is tantamount to intellectual suicide.