The Cartesian argument seems to explicate the fact that I necessarily know that something thinks, and that I necessarily know that something thinks even if I don't checking the world to verify whether something thinks.

Nevertheless, some philosophers deny that we can know anything a priori. What counter-Cartesian arguments have those philosophers propounded?

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    Can you specify who you mean by "some philosophers". There's a lot of different philosophers in history, some of whom might do something you could categorize in this way. – virmaior Jun 13 '15 at 1:26
  • Well, does a baby know that it thinks before experiencing itself thinking? I doubt it. So is it a priori, or based on experience? No one without the experience of thinking thinks that something necessarily thinks. So how do you know you didn't acquire this prejudice from experience? – jobermark Jun 13 '15 at 4:07
  • @virmaior In an essay I read by Paul Bogohssian, he mentioned that the possibility of a priori knowledge was debated. Then he proceeded to argue how some kinds of "entitlement" might justify some innate beliefs; thus giving us a priori knowledge. – Hal Jun 22 '15 at 16:45

Bernard Williams provides detailed analysis of ego cogito ergo sum argument in Descartes, The Project of Pure Enquiry.

The oldest objection to the premise, ego cogito, which goes back to Gassendi, is that the reference to ego ("I") is circular. "Were we to move from the observation that there is thinking occurring to the attribution of this thinking to a particular agent, we would simply assume what we set out to prove." Or as rephrased by Georg Lichtenberg, rather than supposing an entity that is thinking, Descartes should have said: "thinking is occurring". Without ego we are left with cogito alone, so while "thinking is occurring" we can not infer that "something thinks".

Further analysis of Descartes's fallacy reveals other problems. "Through introspection, or our experience of consciousness, we have no way of moving to conclude the existence of any third-personal fact, to conceive of which would require something above and beyond just the purely subjective contents of the mind". In other words, even if we could somehow infer ego from cogito it does not make it a "something" that can be spoken of in the third person, i.e. anything objective that can be known, let alone known a priori. The identification of "I" with an object in the world is certainly a posteriori and empirical. So the thinking, which is occuring, might not be producing any knowing. This is paradoxical, but there is no crime in it against logic.

  • Please note that I intentionally wrote " something thinks " in order to convey that I did not mean to ask a question on the justification of the presupposition of the self in the Cogito. I meant to ask 'even if there is no self, the cogito at least proves that there is thinking. That there is thinking seems impossible to doubt, and seems necessarily knowable a priori. Accordingly, I wonder how can anyone doubt that there is a priori knowledge?' – Hal Jun 22 '15 at 16:51
  • @Hal There may or may not be a priori knowledge, but experience of thinking by itself is incapable of producing it. We think when we dream too, but no knowledge is acquired, knowledge requires a complex of actions, such as forming beliefs, reflection, verification none of which a stream of thinking is obliged to provide, and capacity for which humans only acquire as a result of long practice with plenty of empirical input. Descartes is simply trying to smuggle in all the benefits without acknowledgement by pretending that it is all there in pure thinking. – Conifold Jun 23 '15 at 18:20

I never read about a priori knowledge in the time of Descartes. The conceptuation of a priori comes from Kant, not Descartes.

I think that there doesn't exist any a priori knowledge, every knowledge is constructed. Sometimes some synthetic judgements seem to be a priori but history shows that all of these judgements are, after all, analytic because any formal science is analytic.

In other way the concept of "knowledge" may requires conscience. The best that you can have about "a priori knowledge" are unconscious reactions as reflex, pain and so on... but this is not knowledge, at least I don't consider it.

But in any way there doesn't exist any fallacy on the thoughts of Descartes as someone said before, because circular thinking is legit and valid. This "fallacy" doesn't exist in reality, history proved it a lot of times.

You can have a process where it doesn't care that it is circular, and it doesn't care what happens first: one time the process becomes circular it exists because it is an equilibrium, and there is no "fallacy" in the real world of this processes. In any case what happens is that there exists some level of unknown mechanism.

I recommend about this topic to read, by example, some book of Paul Watzlawick who studied these things in deep.

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