[Matt R.]

Well, OK. You are basically just re-asserting stuff that I disagree with.

"It is pretty obvious that if you were completely deprived of sensory input from birth, you would not have any actually meaningful thoughts."

I don't think this is obviously true at all.

I don't understand how the position that "all knowledge is derived from sensory input" requires NO a priori assumptions. To me, it seems clear that the position itself is an a priori claim. There is nothing in the environment which states "what you see here? yeah, it's definitely absolute truth". It seems, to me, that we must assume our sensory information is accurate.

I must go for the time being. I also think we are arguing in circles, and I honestly don't understand why you think your position requires no a priori assumptions. I will try to get back with you later.