The Second Meditation is subtitled "The nature of the human mind, and how it is better known than the body" and takes place the day after the First Meditation. The Meditator is firm in his resolve to continue his search for certainty and to discard as false anything that is open to the slightest doubt. He recalls Archimedes' famous saying that he could shift the entire earth given one immovable point: similarly, he hopes to achieve great things if he can be certain of just one thing. Recalling the previous meditation, he supposes that what he sees does not exist, that his memory is faulty, that he has no senses and no body, that extension, movement and place are mistaken notions. Perhaps, he remarks, the only certain thing remaining is that there is no certainty.

Then, he wonders, is not he, the source of these meditations, not something? He has conceded that he has no senses and no body, but does that mean he cannot exist either? He has also noted that the physical world does not exist, which might also seem to imply his nonexistence. And yet to have these doubts, he must exist. For an evil demon to mislead him in all these insidious ways, he must exist in order to be misled. There must be an "I" that can doubt, be deceived, and so on. He formulates the famous cogito argument, saying: "So after considering everything very thoroughly, I must finally conclude that this proposition, I am, I exist, is necessarily true whenever it is put forward by me or conceived in my mind."

The Meditator's next question, then, is what this "I" that exists is. He initially thought that he had a soul, by means of which he was nourished, moved, could sense and think; and also that he had a body. All these attributes have been cast into doubt, except one: he cannot doubt that he thinks. He may exist without any other of the above attributes, but he cannot exist if he does not think. Further, he only exists as long as he is thinking. Therefore, thought above all else is inseparable from being. The Meditator concludes that, in the strict sense, he is only a thing that thinks.


The cogito argument is so called because of its Latin formulation in the Discourse on Method: "cogito ergo sum" ("I think, therefore I am"). This is possibly the most famous single line in all of philosophy, and is generally considered the starting point for modern Western philosophy. In it, the Meditator finds his first grip on certainty after the radical skepticism he posited in the First Meditation. The cogito presents a picture of the world and of knowledge in which the mind is something that can know itself better than it can know anything else. The idea that we know our mind first and foremost has had a hypnotic hold on Western philosophy ever since, and how the mind can connect with reality has ever since been a major concern. In this conception, the mind ceases to be something that helps us know about the world and becomes something inside which we are locked.

We should note, however, the distinction between the "I think, therefore I am" as stated in the Discourse on Method and the formulation we get in Meditations on First Philosophy: "So after considering everything very thoroughly, I must finally conclude that this proposition, I am, I exist, is necessarily true whenever it is put forward by me or conceived in my mind." Neither "therefore" nor "I think" appear in Meditations on First Philosophy. The absence of "therefore" is important, since it dissuades us from reading the cogito as a syllogism, that is, as a three-step argument as follows:

(1) Whatever thinks exists

(2) I think

Therefore (3) I exist

The trouble with a syllogistic reading, which Descartes explicitly denies elsewhere in his writings, is that no reason is given why (1) should be immune from the doubt that the Meditator has posited. Also, the syllogistic reading interprets the cogito as a reasoned inference at a point in the Meditator's doubt when even reasoned inferences can be called into doubt.

But if everything is to be doubted, how can the Meditator know the cogito? A number of readings have been given to understand this step. One is to read it as an intuition rather than an inference, as something that comes all at once, in a flash. Another reading interprets the cogito as a performative utterance, where the utterance itself is what confirms its truth. That is, I could not say "I exist" if I did not exist or if I did not think, and so the act of saying it is what makes it true. Thus, I can only affirm my own existence (not anybody else's) and I can only do so in the present tense: I cannot say "I thought, therefore I was/am."

It should be noted that the cogito only works for thought. I cannot say, "I walk, therefore I am," since I can doubt I am walking. The reason I cannot doubt that I am thinking is that doubt itself is a form of thought.

After the cogito, the Meditator advances the claim that he is a thing that thinks, an argument called the sum res cogitans, after its Latin formulation. There are three controversies regarding the claim "I the strict sense only a thing that thinks," which we will examine in turn: whether the claim is metaphysical or epistemological, what is meant by "thing," and what is meant by "thinking."

It is more plausible to read the sum res cogitans as an epistemological remark, saying that, "whatever else I may be, I know only that I am a thing that thinks." However, in some of his writings, Descartes makes it plausible to read him as making a metaphysical remark, that "I am only a thing that thinks." His reasoning might go something like this: "I know that I am a thinking thing, and I do not know whether I am a bodily thing. My body and my mind cannot be one and the same, because I should either know both of them or know neither of them. Since I know I am a thinking thing, and know that my body and my mind are two separate things, I can conclude that I am not a bodily thing. Therefore, I am only a thing that thinks." In so arguing, however, Descartes would commit the so-called "intentional fallacy" of basing an argument on what one does not know. If two things had to be either both known or both not known in order to be identical, we could argue that Bruce Wayne and Batman are not one and the same as well.

"Thing that thinks" also carries some ambiguous baggage. By "thing," Descartes could simply be using the word as we do today, as an ambiguous throwaway word when we don't want to be more specific. More likely, though, he is using it to mean substance, the fundamental and indivisible elements of Cartesian ontology. In this ontology, there are extended things (bodies) and thinking things (minds), and Descartes is here asserting that we are minds rather than bodies. Of course, "thinking" is also highly questionable. Does Descartes mean only the intellection and understanding that is characteristic of the Aristotelian conception of mind? Or does he also include sensory perception, imagination, willing, and so on? At the beginning of the Second Meditation, the Meditator has cast sensory perception and so on into doubt, but by the end of the Second Meditation, sensing, imagining, willing, and so on are included as attributes of the mind. This question is further explored in the commentary on the next section.

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