Descartes: “I think, therefore I am”
Introduction
In the First Meditation (which we discussed earlier this year) Descartes asks the question “What can be known with absolute certainty?” His aim is to establish a secure foundation for all human knowledge. In order to answer this question Descartes introduced the method of doubt. According to this method, if a belief could be doubted then it couldn't serve as a foundation of knowledge - it couldn't be known with absolute certainty. The foundations of knowledge must, according to Descartes, be indubitable. And he argued that all our beliefs about the physical world failed the indubitability test and therefore could not be known with absolute certainty. Two arguments he used were the Argument from Dreaming and the Evil Demon. According to the Argument from Dreaming, all our beliefs about the physical world could be doubted because, for any given perceptual judgement (eg. I'm sitting here by the fire), we have no way of knowing whether or not it is part of a dream. The Evil Demon argument states that we can't be sure about any of our beliefs since we might be deceived be the Evil Demon. In the Second Meditation Descartes tries to show that there is indeed at least one belief which is absolutely certain and immune from the Dreaming and Evil Demon arguments.The Indubitable Belief
Descartes argues as follows:“But I have convinced myself that nothing in the world exists - no sky, no earth, no minds, no bodies; so am I likewise non-existent? But if I did convince myself of anything, I must have existed.” (p. 67) The form of Descartes's argument is: If I convince myself of something then I must exist. Note that this does not depend on what it is that I convince myself, even if it is that in fact nothing at all exists. Descartes continues:
“But there is some deceiver, supremely powerful, supremely intelligent, who purposely always deceives me. If he deceives me, then undoubtedly I exist; let him deceive me as much as he may, he will never bring it about that, at the time of thinking that I am something, I am in fact nothing...... I must conclude that this proposition “I am”, “I exist”, whenever I utter it or conceive it in my mind, is necessarily true.” (p. 67)
Descartes's argument here can be summarised by the famous statement “I think, therefore I am” - this statement is usually referred to as the “cogito”, as shorthand for the Latin cogito ergo sum ( “I think, therefore I am” doesn't actually appear in the Second Meditation. It occurs in the Discourse on Method). What is the cogito meant to show? According to Descartes the cogito forms the bedrock of human knowledge. It is the one thing we can be absolutely certain about. Thus for Descartes, that which is absolutely certain and which forms the basis of human knowledge is our knowledge of our mental states.
Discussion and questions
- Note first of all that when Descartes asserts the cogito he is not stating that it is certain that he exists. There is nothing necessary or absolutely certain about Descartes's existence. What is certain, according to the cogito, is that if he is thinking (or doubting, being deceived, believing, etc), then he must exist.
- Bertrand Russell, amongst others, objected to the cogito, arguing that the use of “I think” was illegitimate. The use of “I think” already assumes that I exist and hence can't be used to establish it without circularity. The premiss of the cogito should be instead “There are thoughts” or “There is thinking”. But then it clearly fails to establish what Descartes wants. What do you think of Russell's criticism? How could Descartes reply to it?
- Is the cogito an inference? If so, what sort of inference is it? Is it like this:
Whatever is thinking must exist.
I am thinking.
Therefore, I exist.
But what does the first premiss of this argument really mean? It has the same form as “Whatever is thinking has a brain”. But generalisations like this presuppose existence in that they imply “If there is something which thinks then it has a brain”. However, in that case the premiss “Whatever is thinking must exist” will imply “If there is something which thinks then it must exist” which is like saying “If something exists then it exists”. So if the cogito is an inference then it can't have the form mentioned above. What form could it have? - Why state “I think therefore I am” and not “I walk therefore I am” or “I breathe therefore I am”? Is my existence revealed more fundamentally in my thinking than in my walking or breathing?