James Conant distinguished between "Cartesian skepticism" and "Kantian skepticism" ("Varieties of Skepticism"
). Each has many criteria, but roughly, the Cartesian skeptic considers what ought to be required to have knowledge and finds it lacking in even the most ordinary case, whereas the Kantian skeptic looks at, say, knowledge [though Kantian skepticism can apply to a vast range of topics], and is simply baffled as to how it is even possible. For the Cartesian "it looks as if there is something we cannot do
," whereas for the Kantian it "looks as if there is nothing to do
(not even dream), where we had previously thought there was something" (107/111).
I'd like to put a finer point on Kantian skepticism. I think the simplest incarnation of the Kantian skeptic (sorry, Kant) is the Tortoise, from Lewis Carroll's "What the Tortoise Said to Achilles"
. Presented with a simple inference, the Tortoise asks for further justification, to which Achilles can only respond by providing another inference, for which the Tortoise again demands further justification, ad infinitum. The Tortoise accepts nothing as basic. This is not unlike the difficulty of justifying an inductive inference without appealing to induction. Our Tortoise might as well be asking the Kantian question, how is modus ponens
If this is the right way to think of Kantian skepticism, or Kantian questions, they start with an inability to see something as 'basic' (as 'bedrock') which must be seen as basic, or, perhaps, with a question that cannot be answered or phenomenon that can't be explained from within the framework in which it's asked. More modus ponens
inferences will not enable the Tortoise to understand modus ponens
inferences. What will help the Tortoise? --Some other kind of explanation. Probably exercises in aspect-perception. Phenomena as basic as modus ponens
invite puzzlement; it's natural to want to know why they work. That which must be taken as basic invites the need to understand it the way we understand everything we understand through it.
Other predicaments that inspire Tortoise-like responses:
- basic actions--how do we make them happen?
- induction--how do we justify inductive inference?
- how do we know our own mental states?
- in what does following a particular rule consist?
There is more to each of these, of course, even by way of large patterns. For instance, I think it's helpful to think about both the problem of justifying induction and rule-following as drawing on an inevitable switching between foreground (a given instance or something that conforms to the inductive law or of following a rule) and background (the entirety of the inductive law, the entirety of the rule--which both cover an infinite number of cases).
I will not pretend otherwise: for me, all interesting philosophical questions are Kantian questions. I'm not sure I can defend this preference, except to say that a concern for what can be explained and how concerns inquiry in all domains--not simply philosophy; though wherever it arises, it is philosophy.