How Can You Prove You’re Real And Not Some Evil Genius Demon’s Figment of Imagination? – VIDEO


How do you know you exist? It's a simple enough question, but the answer is a little more tricky. After all, how do we know we aren't dreaming? Or that some evil genius demon hasn't tricked us into believing that "reality" is "real"?  

A new TED video helps break down these questions of existence – leading us towards Descartes' famous philosophical conclusion: I think, therefore I am.

Check it out, AFTER THE JUMP



  1. Hislv says

    there are 2 fundamental flaws to Descartes “Cogito ergo sum”

    1.) Why can’t an illusion have thoughts? Descartes doesn’t actually prove the existence of any being. You could still be an illusion, even if you are perceiving thoughts. For example: “I” might “be” someone else when I am dreaming, and “I” might have thoughts in this dream. However, this does not mean that this “being” that I “am” in the dream is real. It is still an illusion. There is no reason why we can’t be illusions in “real” life, and still have thoughts.

    2.) This does not prove that the thoughts are not an illusion. In order for Descartes’ arguments to hold any weight, he must be able to prove that the thoughts that one perceives are not illusory. If the thoughts of a “being” are illusory, then it follows that the “being” itself is illusory.

  2. kipp says


    Is the Towleroad comments section really prepared for this kind of metaphysical esoterica?

    There are problems with the cogito, but they are not quite as you describe.

    The main problem of the cogito is insufficiency: The most Descartes can really get from the experience of thinking is that “there is thought”, rather than “I think” – He isn’t entitled to assume an “I” merely because thought exists. Saying “I think” is implicitly asserting there is an I. You cannot prove a conclusion by stating it as a proposition.

    Illusion is not the problem here: Thoughts are still thoughts whether they are illusory or not. The contents of thought may be mistaken or illusory – but the thought itself is still “real.”

  3. Greg says

    I would say that the Cogito is flawed, more simply, because it presupposes a self that thinks in order to prove the existence of the self. I don’t know the terminology, but I’m guessing there’s a degree of tautology involved. I admire Descartes’ innovative attempt to go back to basics, very impressive for his time, but he fails at the last moment with this argument, perhaps tempted by the neatness of the Cogito.

  4. radioredrafts says

    If you think “I”, you are confirming to yourself “I am”. One doesn’t think without being. If you complicate this idea, you’re down the rabbit hole.

    Or, as “they” say: the further you go, the less you know.

  5. kipp says


    Your sentiment is Descartes’ notion in more colloquial language. Its flaw is the assumption that the only source of thought is an “I” – and that only an “I” can perceive of thoughts. We’re talking about basic beliefs – whether an “I” exists at all. You cannot justify your own existence by *assuming* that thoughts require an “I” to think them.

    If you know as fact that thoughts require an “I”, you can justify the conclusion… but that’s the question itself: Is there such a thing as “I” in the first place.

  6. Bill says

    @ 1♥ : The holographic principle refers to a property of the mathematical formulation of string theory. The interesting thing is a mapping between string theory and general relativity – there’s a compelling argument (proven in some cases) – that this works. Such transformations are frequently used in physics and engineering because the transformed problem is sometimes way easier to solve. Finding such a transformation is, of course, nearly always interesting. Of course, when it gets into the popular press, “The universe is a hologram” sounds a lot more interesting that “isomorphism discovered connecting string theory and general relativity”

    A simple example of why such mapping are useful is the analogy between mechanical systems with springs, dampers and masses, and electrical system with inductors, resistors and capacitors. The analogy exists because both are described by second-order linear differential equations. Before we had cheap digital computers, analog computers were used to model such mechanical systems. These allowed you to plug an electrical circuit together that modelled a mechanical system. It was far quicker than building a mechanical model.

    As another example, Fourier and Laplace transforms are used in many areas because they turn differential equations into algebraic equations.

  7. Sergio says

    This is probably the most thoughtful thing Towleroad has ever posted. It’s also nice to see TED stop being so frivolous for once.

    Suggestion for next cognitive science / philosophy of mind post: anything from Nick Bostrom.

  8. anon says

    This is the most solid result in all of rationalist philosophy. The problem with Cogito is that the implications are very limited. You know you exist, but nothing else. The true nature of your existence you cannot know. Descartes spent most of his time trying to extend Cogito all the way to proving the existence of God, but that part of his work is considered a failure.

  9. james street james says

    A rock doesn’t think, and yet, there it is.

    I look in a mirror, and there I am!

    “I think therefore I am” says something about being conscious, not about existence.