QuestionsWho am I, really?I am a thinking thing, and I stay the same
Who am I, really?A soul

I am a thinking thing, and I stay the same

"I am only a thinking thing"

René Descartes 1596 · 1650Doubt everything to find what survives doubt.
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What it claims

I am, precisely, only a thinking thing, that is, a mind, and this mind stays the same under all my thoughts.

Why

I can doubt my body but not that I think; like the wax, what remains through all my changes is the thing that thinks.

In short

"I am a thinking thing, and I stay the same" is an argument by René Descartes (Meditation II, 1641) on the question "Who am I, really?" (answer: a soul). Its claim: I am, precisely, only a thinking thing, that is, a mind, and this mind stays the same under all my thoughts. According to AskPhilosophy's logic check (Z3 solver), the argument is valid only if one grants a premise the author leaves unstated (P2, P5). AskPhilosophy presents 3 objections, 3 of them with a documented reply, and the original text behind each premise, checked word for word.

Meditation II, 1641
Valid with an implicit premise

Once the cogito is secured, Descartes asks what this "I" is of which he is sure. He removes everything he can doubt: the body, walking, nourishment, sensation. One thing resists: he thinks. He concludes that he is "precisely" a thinking thing, that is, a mind. This "I" does not depend on what he happens to be thinking: as wax stays the same wax when its shape, smell and colour change, the mind stays the same when its thoughts change. Note: this link between the wax and the self is a reconstruction. Descartes describes the wax to show that the mind knows it better than the senses do; the unity of the mind under its thoughts is stated elsewhere, in Meditation VI.

P1I can suppose that I have no body and that my sensations are illusions. Of everything attributed to the soul, only one thing cannot be taken away from me: thought.
P2 · implicit premiseWhat cannot be taken away from me without my ceasing to be is what I am.
P3A piece of wax stays the same wax when everything the senses noticed in it changes: taste, smell, colour, shape, sound. What remains is therefore none of those changing qualities, and it is grasped by the mind alone.
P4My thoughts and faculties vary: I doubt, I will, I sense, I conceive. But they are not parts of me: it is the same mind, entire, that wills, senses and conceives.
P5 · implicit premiseThe self is in the case of the wax: what stays the same under the variety of my thoughts is the thing that thinks, not this or that thought.
Therefore I am, precisely, only a thinking thing, that is, a mind, and this mind stays the same under all my thoughts.

click a premise to reject it

If you accept every premise, logic forces you to accept the conclusion. So the debate is about the premises.
Checked by a logic solver: the premises cannot all be true while the conclusion is false.
Without the implicit premise: Without P2 and P5, the computer finds a case where it is certain that I think, the wax stays the same, my mind has no parts, and yet I am not a thinking thing that stays the same: nothing rules out that "I" is something other than what I know about myself.
The argument is valid with P2 and P5, the two steps Descartes does not state in this form. Without P2, nothing says that what resists doubt is what I am, and not merely what I know about myself. Without P5, the step from the wax to the self is missing: the wax shows that a thing can stay the same under changing qualities, not that the self is such a thing. P4 (Meditation VI) gives Descartes the idea of a mind without parts, one and entire.
Analogy. A play can change set, costumes and music at every act and still be the same play. You do not find it in any one of the sets: you understand it by following what remains. For Descartes, the self is like the play, and my thoughts like the sets.

Objections

3

Each objection is a conversation: click to see who replies and where the debate stands.

Pierre Gassendi 1641 · attacks premise 2

You observe that you think, nobody denies it. But you still have to prove that thinking is so far above the nature of body that no body, however fine, pure or agile, could be capable of it. Nothing shows that you are not a very subtle body.

Descartes replies
see the argument
Descartes Descartes's reply
Descartes answers that in Meditation II he only asserted what he knows: as far as he knows himself, he is nothing but a thinking thing. He had no need to admit that this substance is a subtle body, having no reason to believe it; if Gassendi has one, it is for him to give it. Demanding that Descartes prove it false is like telling someone who says he is in Holland that he must prove he is not in China.
Where the debate stands (our summary)The core disagreement is about the burden of proof. For Gassendi, one must show that thought goes beyond any body; for Descartes, one should accept only what one knows clearly, the real distinction between mind and body coming later (see the link). The debate between dualists and materialists on this point remains open.
John Locke 1694 · attacks the conclusion

Whether it is always the same substance that thinks does not concern the identity of the person. If it is the same consciousness, different substances may be united in one person. What matters for the person is consciousness, not the thinking thing that carries it.

a defender replies
see the argument
No reply possible: objection raised in 1694, after the author's death (1650).
Thomas Reid defender of the argument · 1785
Reid takes up Locke's definition: a person is an intelligent being, endowed with reason and consciousness. He draws from it that as long as this intelligent being continues to exist and to think, it is the same person. To say that the person ceases to exist while the intelligent being continues would, for him, be a manifest contradiction.
Where the debate stands (our summary)Locke and Reid differ on the meaning of "same person": for Locke it is the same consciousness, whatever the substance; for Reid the person is the thinking being itself, which continues to exist. The core disagreement: does a person's identity rest on a psychological link or on the continued existence of one and the same thing? An open point, with no widely accepted answer.
David Hume 1739 · attacks premise 5

When I enter most intimately into what I call myself, I always stumble on some particular perception or other, of heat or cold, light or shade, love or hatred, pain or pleasure. I never catch myself without a perception, and never observe anything but the perception. For him, the self is nothing but a bundle of perceptions.

a defender replies
see the argument
No reply possible: objection raised in 1739, after the author's death (1650).
Thomas Reid defender of the argument · 1785
Reid writes that our thoughts, actions and feelings change every moment, but that the self to which they belong is permanent: I am not a thought, I am what thinks, acts and suffers. The thinking being has a continued existence, and we have an invincible belief that it stays the same when all its thoughts change.
Where the debate stands (our summary)Hume finds that, looking inward, he meets only perceptions, never a self that carries them. Reid answers that this self is not one more perception but that to which all perceptions belong, and that we believe in it naturally. The core disagreement: is a bearer of thoughts needed, or is the bundle of perceptions enough? An open point, with no widely accepted answer.