Something about my translation has bothered me since I originally posted my question (which follows below). It concerns what Bertrand Russell wrote in "On Denoting". Ryno indicated a circularity with the way I originally reformulated Cogito ergo sum. But upon rereading Russell I'm wondering if the following isn't a more accurate formulation:

  1. There exists an x such that x is Descartes.
  2. For any y that is Descartes, x and y are identical.
  3. For any z, if z is a time at which Dx thinks, then at z, Dx exists.

Why is it important? Because it would lend weight to the identity component of my original question. I appreciate any comments anyone might have.


Suppose we were to reformulate Cogito ergo sum to read: "For any I, if at some instant in time I thinks, then at that instant I exists."

EDIT: Please feel free to substitute "at some instant in time" with "over some unspecified range of time straddling some instant."

Wouldn't Descartes have to establish the identity of the subject I for any two distinct instants in (or ranges over) time at which the statement is true? What I have in mind is Leibniz's law, which states that entities x and y are identical only if each has exactly the same properties -- and in what sense can the I at times t1 and t2 be said to have exactly the same properties?

I know relevant questions of personal identity have been addressed by Derek Parfit, but I suppose the essence of my question concerns what implications there are (if there are any) for Cognito ergo sum should we accept Leibniz's law.

If Descartes doesn't have to establish the identity of I at times t1 and t2, then what does that say about the kind of thing Descartes' I is?

  • 1
    Should that formulation not be: For Any given "I", if I thinks (at some point in time), then it exists (at that point in time)?
    – Ryno
    Oct 22, 2012 at 8:36
  • Just to add to the above - this also avoids having to start "There exists an I" and finish with "I exists" - which sounds circular to me...
    – Ryno
    Oct 22, 2012 at 8:37
  • Ryno, I believe you're right, thanks. I've edited the text accordingly.
    – user2581
    Oct 22, 2012 at 14:33
  • proposing: I --> []I As the cogito expressed in modal logic. Does it work?
    – Dave L.
    Oct 7, 2013 at 2:09

2 Answers 2


f Descartes doesn't have to establish the identity of I at times t1 and t2, then what does that say about the kind of thing I is?

I don't think the identity of I at times t1 and t2 is relevant to Descartes's project in the Meditations. Remember, the Cogito does not exist in a vacuum; it forms a part of a specific argument.

  • Ah, perspective check. Thanks, that works for me.
    – user2581
    Oct 23, 2012 at 14:14

I would amend that to say that for an unspecified range of time straddling the instance, he/she exists. Otherwise we risk an unmotivated dichotomy between thinking and not existing.

If the experience of existing contains the experience of existing through time, then I do not think it can be isolated only in those instances of thought or awareness of thought. Just that an existence requires existence without thought, as is modeled for us by a rock's case that it exists.

That better meshes the sense of what Descartes was saying with a more analytic approach. However, no such statement can be analytic. Instead, it is an irreducible or axiomatic. To the extent that any of us can contemplate what Descartes is saying, we must also exist. This even partitions seeming actors.

Take for example the movie, A Beautiful Mind, to the extent that we could argue that John Nash's "friend" Charles comprehends--and doesn't simply appear conversant in Descartes--then he exists. To the extent that we count him a figment of Nash's imagination, any comprehension he appears to have of Descartes is the same as Charles appearance to Nash. It simply a detail in the projection that Charles is Nash's college roommate and could discuss such things.

The middle case is that in that there is a part of Nash's brain or psyche would could be said to be Charles, then Charles "exists" to the extent that he represents an alienated comprehension apart from Nash's normal set of thoughts.

  • Hi Axeman, I edited my question in light of your helpful comments.
    – user2581
    Oct 23, 2012 at 1:39

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