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"Cogito, ergo sum", "I think, therefore I am", said Descartes but how does one know that one thinks? Could "my" thoughts not be part of an illusion of someone/something else? Can "I" actually know that "I" exist?

I apologise if this question has already been answered (didn't find anything here or Google) or makes no sense and if my English is poor.

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  • Your thoughts do not belong to "I", they in fact are the function, product of something else - (your) consciousness. Reflective consciousness (i.e. consciousness supposing consciousness) sees the thought being thought as an object, and it produces an illusory second object "who must be thinking it", the Ego (I).
    – ttnphns
    Commented Jan 21, 2018 at 21:17

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Relevant SE link: "I think, therefore I am" - How does "I" establish "I" before "I" can "think"?

how does one know that one thinks?

Because something that doesn't exist can't think. Therefore you must exist (or rather I must exist, as I can't say anything about you beyond what my senses tell me is the case). If I didn't exist, then I couldn't be thinking. It is an absolute incoherent statement to say that I can think and not exist at the same time. We can't even begin to try to give a rational argument to justify such a position.

What form I exist isn't really knowable with certainty. Am I part of a dream? Maybe. Or perhaps I am a brain in a vat or in a supercomputer simulation of our universe, and my essence consists of nothing more than binary coding. Entirely possible.

What Descartes wanted to do with The Cogito was to start with a foundational philosophy rooted in the certainty he saw in self-doubt. Using it as an edifice to establish the rest of his philosophy. A lot of it was supported by the Christian God not being an "evil deceiver" tricking him into believing he was experiencing what he was experiencing through his perceptual apparatus.

Reference:

Brueckner, Tony, "Skepticism and Content Externalism", The Stanford Encyclopedia of Philosophy (Winter 2016 Edition), Edward N. Zalta (ed.), URL = https://plato.stanford.edu/archives/win2016/entries/skepticism-content-externalism/.

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Suppose Descartes' Evil Demon exists. Why can't I and my thoughts be merely dreamt or fantasied by the Evil Demon ? I can imagine, now, a person, X, who in my imagination is thinking all sorts of things. Only, of course there is no X and X is not thinking anything. X is purely a creation of my imagination. Why can't I and my thoughts be equally unreal products of the Evil Demon's dreams or imagination ?

Do not suppose that I endorse the existence of Descartes' Evil Demon (malin génie). I am only probing logical possibilities, or what I take to be such.

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