UhOH wrote:Recently I have been wracked by global scepticism, are we brains in vats, were the world and all our memories created last Thursday etc. I found that with the use of certain logical tools like Ockham's razor and abductive reasoning that I could dispel some of these sceptical doubts. But how do I know that my reasoning is true? How do I know that there isn't, say, a 100% probability that we are brains in vats? Couldn't I expand this to be more general as well, how do I know whether my deductive reasoning is valid? How do I know if any of my reasoning is true at all?
Global scepticism ceases to be compelling when you understand that its arguments are either implicitly self-contradictory or depend on the unfounded presupposition that we don't experience the world directly, but experience only our "representations" (sense data, qualia, etc.), and that we have to use those to
guess at an external world.
Re. the brain in a vat, for example, there are several types of answer, depending on how the question is posed. Firstly, and generally, the brain
is of course perceiving the external world (in the form of the impulses), the diabolical scientist is simply messing with the input. Brains, vats, mad scientists, computers, etc., are themselves objects in an external world, so they can't be used to cast doubt on the possibility of one, or on the possibility of demonstrating one.
And as for yourself, if someone asks you the question personally, or just generalizes it to Cartesian-Demon-like scenarios, or to "how do you know that the situation is not x logically possible scenario?", the proper response is that what is "logically possible" is so far merely
imagination, and is there any reason to take that imagined scenario seriously as
possible?
Also, of course, your interlocutor exists and is asking you these questions, so he's shot himself in the foot before he starts. If he suggests there's no reason why he can't be a "dream interlocutor" posing the question to a solipsistic you, then you have to ask him in what sense your experience as a whole can be "dream-like" in any meaningful way, when it bears no hallmarks of dreaming and cannot be contrasted with anything else
in your experience (as dreams, normally understood, contrast with waking).
When you boil it right down, all these pseudo-problems arise from taking up the Cartesian methodologically solipsistic starting point of, "What can I know for certain?" in a certain way. If you ask that question while bracketing an external, shared reality, all you end up doing is having a nagging hankering to redefine "experience", "consciousness", etc., as things that only I can have.