I've heard it postulated by some people that "we can't truly know anything". While that does seem to apply to the vast majority of things, I can't see how 'cogito ergo sum' can possibly be false.

No matter what I am, no matter in what way I'm being tricked, no matter how I may be deluded, I must exist in order to - in some way - be considering this right now (or be being tricked right now).

Is 'cogito ergo sum' necessarily correct, or have I missed something?

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    It was helpful to me to recognize there is a degree of irony in his formulation: Descartes is arguing, then, that doubt itself can be an absolutely firm foundation for knowledge. That is, knowledge itself is hereby founded on this very paranoia-about-knowing-anything-whatsoever ;)
    – Joseph Weissman
    Commented Jun 7, 2011 at 22:37
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    I answered this question as a part of an answer to a related question: philosophy.stackexchange.com/questions/206/… Commented Jun 8, 2011 at 18:47
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    Cogito ergo sum -- is a single most important achievement of humanity, as a civilization -- which are not that many. If humanity will pass away, i propose to write "Cogito ergo sum" on its grave!
    – Asphir Dom
    Commented Feb 23, 2014 at 21:03
  • Too many answers to bother making a full answer about this. But it is said that not only is it a delusion, but it is the fundamental delusion.
    – dgo
    Commented Jun 17, 2014 at 2:56
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    This very statement is a prime example of the ego of humanity. The admission of knowing nothing, in and of itself is saying we know something - the fact that we know nothing. The illusion this statement is significant for one who is classified as genius only furthers the significance of how pompous this truely is. Presenting a linquistic paradox as a statement you are more elightened because of this privy knowledge, is severly inverted. Commented May 14, 2018 at 11:27

22 Answers 22


The objection to "I think, therefore I am" is that it presupposes the existence of an "I" doing the thinking. Possibly, "there are thoughts" is the true minimum statement that can be reached using Descartes' method; this does not presuppose the existence of some sort of unified consciousness having the thoughts.

Bernard Williams and Søren Kierkegaard were early objectors to presupposing "I".

That said, cogito ergo sum certainly has a stronger basis than the rest of what Descartes built on it with the Cartesian Circle.

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    +1 In addition, it presupposes that a proposition or fact and its negation cannot be both true. And that existence is a meaningful term. Etc.
    – Cerberus
    Commented Jun 8, 2011 at 2:20
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    As someone who researches artificial intelligence via genetic algorithms of neural networks, I also have to question what it means to "think" or what "thoughts" are. The Chinese room is often taken as a refutation of the intelligence of artificial intelligences, but the same arguments used to deconstruct artificial intelligences can also be applied to natural ones. Commented Jun 8, 2011 at 12:26
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    +1 It's worth noting that this answer argues not that cogito ergo sum is false, but that it is a circular argument. Philosophical skeptics may, of course, reject the proposition. (But that at their own peril!) Commented Jun 8, 2011 at 18:38
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    @Jon: indeed, "I think -> I am" is True if "I think" is False, although I took the OP's question to be more whether Descartes' argument is a sound one than if the particular compound logical statement is True.
    – Wooble
    Commented Jun 8, 2011 at 18:43
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    I would say "there are experiences". The thoughts are very hard to objectively distinguish from hearing. It might not be thoughts, but just a recording. ;) Commented Jun 29, 2011 at 7:33

This is exactly what Descartes was trying to prove. He wanted to build philosophy from the ground up based on a series of rational observations. I think he must've been quite dismayed when he realized that it is possible to take a skeptical position on almost everything.

His conclusion in his Meditations I & II was that this is the only truth, and the only thing we can know for absolute certainty. Whether this is true or not depends on how convinced you are by his Meditations.

The phrase is not without its critics, but I think it's a matter of semantics. Let me explain:

The essence of his argument is that you can doubt almost everything about the world, but you can't doubt that you're doubting. Because if you doubt that you're doubting, you're still doubting. This is why the phrase is sometimes seen as 'I doubt, therefore I am.'

Most of the contention comes from trying to place meaning to the words 'I' and 'exist'. Perhaps it is not me who is doubting, but there is still doubt. I tend to prefer the more constrained version: 'There is doubt.' This statement avoids a lot of the semantic ambiguity, but connotes a weaker argument.

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    Precisely. Ripped from its context, cogito ergo sum is nothing more than a funny puzzle. In context, it's a powerful attack on extreme skepticism. The thinker who opposes it "vanishes in a puff of logic". Commented Jun 8, 2011 at 18:44
  • It's more of an axiom than a proof. While you can't doubt that you're doubting, it doesn't entail that you exist. Seems almost absurd to question whether or not you exist, but it remains that there's no link from doubting your ability to doubt and existing. If this were the matrix, your "doubt" could be the result of a complicated cognitive program, however to say you exist would be to say that your program exists. But then you have to redefine existence.
    – Neil
    Commented Jun 29, 2011 at 12:14
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    Good post. There is an update from Descartes - "Sentio ergo sum!"
    – Asphir Dom
    Commented Feb 23, 2014 at 21:18
  • If "there is doubt" is enough to establish existence (of doubt presumably) then it is the same kind of "existence" that can be ascribed to round squares on the same grounds. It sounds superficially satisfactory only because of implicit thought that even if the doubt is "unreal" to be unreal there has to be something "real" underlying it, and that exists. This extra argument is a fallacy, and without it there is nothing but spurious use of "existence".
    – Conifold
    Commented Sep 7, 2015 at 23:36
  • @Conifold it isn't the mere assertion that makes it correct. i think you may have it backwards: "doubt" exists in the same way "rounded squares" cannot exist; that is, the converse would defy logic. if you are stating that we cannot trust logic, i think you are making the same point as LennartRegebro in his answer
    – Jeff
    Commented Sep 8, 2015 at 0:02

Yes it may be false

I think therefore I am is a logical conclusion, aimed at showing that something exists. It assumes that logic works and exists. How can you assume that before you even know if you or anything else exists?

Well, you can't, of course. And famously logic is in itself impossible to prove. Therefore we can not say that Cogito is proven beyond all doubt, and hence it still may be false.

It is however an untenable position to claim that you do not exist, but that is another question.

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    This is true for that specific formulation of Descarte's actual position. However, I think it would be fair to point out that his starting point was closer to "something exists that something experiences as I" and does not rely on the validity of formal logic.
    – philosodad
    Commented Jul 4, 2012 at 8:02
  • There are passages in Descartes' work that suggest another reading, namely, that the "ergo sum" isn't a syllogism but another intuition, as basic as the "cogito". I found it in The Cambridge Companion to Descartes, Peter Markie's essay The Cogito and its importance.
    – iphigenie
    Commented May 3, 2014 at 16:56
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    Descartes explicitely envisage that he may be deluded in thinking that his reasonning is trustful so it's not a matter of logic here, but a pure intuition "I am, I exist". Commented Oct 7, 2014 at 12:40
  • Which means he should have simply said "I exist, I think". Commented Oct 9, 2014 at 13:13
  • The statement "It is however an untenable position..." is vacuous. The non-existence of that which you call "yourself" and the "world" is a very interesting (and highly probable) possibility. Have you see "The Matrix"? watch it again. Commented May 28, 2021 at 21:33

Not only could it possibly be false, but there exist two-and-a-half millenia's worth of Buddhist philosophy attempting to draw out the implications of its falsehood.

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    Could you provide maybe a summary of their drawn implications? Or at least a reference where one might look to find these? This answer is kind of a "stub" right now. Commented Aug 20, 2011 at 16:22
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    That's kind of like asking for a reference where one could find a summary of Western Philosophy from Socrates to the present. One of the core teachings of Buddhism is the "no-self" principle (anatta or anatman)-- so literally all Buddhist philosophy grapples with this. But, if forced to provide one reference, I guess I'd point to Peter Harvey's "The Selfless Mind" (books.google.com/books/about/…) Commented Aug 21, 2011 at 9:27
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    Buddhism says there is no self as a continuing objective entity (everything changes) but Descartes' transcendental ego is not necessarily a persistent self Commented Oct 7, 2014 at 12:45

Is 'cogito ergo sum' necessarily correct, or have I missed something?

One way to understand the cogito is as a way to state that it is sufficient to know one has doubts (is doubting) in order to conclude one exists. Now, while I am not certain he would claim it is "necessarily" correct, as you may know, Descartes also considers the problem of whether, essentially, there is a "glitch" in existence -- he formulates the question as that of an evil genius capable of making him believe he was experiencing a world (when in fact he wasn't); Descartes resorts ultimately to God's beneficence in order to surmount the problem, asserting essentially that God wouldn't allow such a wholesale and gross deception.

In other words, the basic metaphysical question involves whether or not the world as we experience it is "real"; one way of expressing the cogito in this context is to read Descartes suggestion as asserting that we are, at least, as real as our doubts about reality; that this much at least is sufficient to indicate proper existence. This may all seem somewhat naive to us today, so it may be helpful as I suggested above to recognize a certain degree of irony in the formulation and theoretical context of the cogito: Descartes is founding our knowledge of the reality of the world on our thoughts and in particular our doubts about the ontological status of existence.


If by existence you mean being different than nothing and be able to perceive the reality, than I hardly believe cogito ergo sum is false.


The only problem that I see with this statement is the definition of "I".

Recent experiments and observations of people with brain injuries very clearly show that our concept of identity is largely a simulation.

So, yes, something exists, but you cannot even conclude that you have a good insight into your own thoughts and motivations.

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    So really, to be necessarily true, the sentence must be expanded to, "I experience something ergo something exists." :-)
    – Jez
    Commented Jun 7, 2011 at 22:21
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    @Jez except that statement presupposed an 'I'! perhaps 'something experiences something ergo something exists'. doesn't quite have the same ring to it though.
    – Jeff
    Commented Jun 7, 2011 at 22:41
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    Can you substantiate your statement, "Recent experiments and observations of people with brain injuries very clearly show that our concept of identity is largely a simulation"? I have not heard of these experiments, but the idea is very interesting to me. Commented Jun 28, 2011 at 18:33
  • +1 for an interesting point of view. The definition of "I" has gotten increasingly blurred since the time of Decartes. Those suffering from multiple personality syndrome have more than one "I" or is it the same? Computer programs capable of holding conversation with you can properly use the word "I" with any real meaning?
    – Neil
    Commented Jun 29, 2011 at 12:19
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    @Phira I also want to know. (smartcaveman)
    – Secret
    Commented Oct 30, 2013 at 13:08

I love a good puzzle and Descartes gave us one for the ages. The challenge is extracting meaning from "I" and "existence" from the thought experiencing it, without presuming either. So what if we define it within the problem context? With a definition, the presumption (and logic problem) could go away ..

Let's try:

  • Thoughts occur
  • Occurence requires a priori spatial and temporal context, which we'll define as "existence"
  • Thoughts that occur in a local, familiar context we'll define as "my" thoughts, which "I" by definition can claim as my own as they have occurred to me, making me a container for my own, familiar thoughts
  • Existence of my familiar thoughts implies that I exist

Besides being a fan of Descartes, I am a fan of Wittgenstein. The latter made it clear how easily we trip on undefined terms.

Descartes's Cartesian Circle makes it clear that he had no issues with the irony of ambiguity and circular reasoning. But if we define key terms to establish context, can't we remove Descartes circularity and provide weight to his original claim?

  • Doesn't his original claim has its basis in circular reasoning. Strip that away and we are left with nothing, right?
    – How why e
    Commented Jan 12 at 22:21

No, the Cogito cannot possibly be proved wrong, even though many philosophers throughout history argued exactly that. However, most philosophers got the Cogito wrong.

There are two main ways philosophers got it wrong in their interpretation of the Cogito, usually to arrive at the irrelevant conclusion that it was not a valid argument.

The first way to get it wrong is indeed to take the Cogito as a logical argument! It is not. The Cogito is not meant for anyone to prove in a logical way the existence of their own mind to somebody else. Indeed, the fact that someone thinks is not apparent to anyone else. Someone saying "I think, therefore I am" merely shows to other people that this person speaks. This in itself could not possibly be a logical proof that the "I" of this person is thinking, let alone that it exists at all. Descartes himself didn't mean the Cogito to be used to assert to the rest of the world the existence of one's own mind.

The other way to get it wrong is to take the Cogito to be about the existence of the self. The self is this psychological phenomenon whereby a subject has a sense of their own biographical identity persisting over time, hopefully throughout life. Although Descartes' discussion of his notion of extreme doubt, leading to the Cogito, is suffused with the notion of self, the notion of self is irrelevant to the Cogito itself.

The Cogito doesn't say "The self thinks, therefore the self exists". This would be a valid argument but one whose premise couldn't be proved true. Instead, the Cogito is expressed in the first-person: I think. And Descartes took the time to explain carefully what was the subject, the "I". The I in the Cogito is the thinking thing. Not the self. Not Descartes. Not a person. Just the thinking thing. The thing doing the thinking.

Thus, the Cogito, if it was a simple logical argument, would be circular: The thinking thing thinks, therefore it exists. But it is not a simple logical argument.

Descartes' Cogito is not a stand-alone metaphysical claim. It is part of Descartes' discussion about body and mind, and more generally Dualism.

He starts by justifying his notion of extreme doubt leading to his conclusion that he is able to doubt even the existence of his own body.

The Cogito, then, is the expression of his conclusion that he cannot similarly doubt the existence of his own mind, because doubting is indeed thinking and thinking implies the existence of the thinking thing, the "I" of the Cogito.

So, as part of this reasoning, the Cogito, rather than a logical argument proving the existence of human minds to the world, is the realisation that one cannot doubt, coherently, the existence of one's own mind.

The Cogito is often misunderstood, and indeed has been often misunderstood throughout history by many philosophers only too anxious to dismiss the Cogito as what they took to be an argument about the existence of the human soul.

You cannot prove the existence of your mind to other people. Whatever you do or say, someone else can reasonably and rationally doubt the existence of your mind. The Cogito doesn't solve this question and wasn't meant to solve this question. Yet, the Cogito is the perfect expression of the fact that no one can coherently doubt the existence of his own mind.

The Cogito is thus a very peculiar kind of argument, and Descartes himself tried to preclude the argument being understood as a logical inference. Something which also explains why the argument has often been misunderstood.

Thinking the Cogito is in effect a performative argument. Any mind thinking the Cogito formally proves its existence to itself. As such it is a fact. Rather than an ordinary argument, it is the expression of a self-demonstrative performance.

I think whenever I perform the act of thinking. Thus, the premise "I think" becomes true, and can be made true, each time I perform the act of thinking. And this, in particular, whenever I think the Cogito itself. Each time I think the Cogito, the premise "I think" becomes true, and with it, the conclusion that I exist.

Bodies don't need to prove to themselves that they exist. If they do, so be it. If they don't, who cares?

The success of the Cogito, possibly the most well-known philosophical argument the world over, comes from its total unassailability in the face of the routine denial of the reality of minds. You can't prove the existence of your mind to somebody else. But whatever other people may say, the Cogito is the expression of the fact that you cannot coherently doubt the existence of your own mind.

This is all that the Cogito is about. The fact that we cannot coherently doubt the existence of our own mind. This is also the force of the Cogito. Nobody would need to pay any attention to Descartes merely asserting the existence of his own mind. Yet, each human being thinking the Cogito will be ipso facto incapable of doubting coherently the existence of their own mind. The mind understood as "the thinking thing".

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    Thanks for this great explanation. I honestly never thought of it like this. especially the concept of "performance". I'll have to cogito on that for a while!!! Commented May 28, 2021 at 21:39
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    @JohnHenckel Appreciated! Commented May 29, 2021 at 9:49
  • "[the Cogito] is not [a logical argument]. The Cogito is not meant for anyone to prove in a logical way the existence of their own mind to somebody else"- those two things aren't that closely related. An argument can be an argument even if it can only be applied to oneself. It doesn't need to be able to prove things to others (although it can presumably prove their existence to them).
    – NotThatGuy
    Commented Sep 5, 2023 at 7:50
  • "the Cogito, if it was a simple logical argument, would be circular: The thinking thing thinks, therefore it exists" - more generously, I'd say it's "thinking is happening, therefore a thinker exists". That sounds like a more reasonable argument, but whether that is still circular I cannot decide.
    – NotThatGuy
    Commented Sep 5, 2023 at 7:50
  • @NotThatGuy "It doesn't need to be able to prove things to others" An argument is used to prove a conclusion. We don't need to prove our own existence to ourselves. We already know. So we don't need the Cogito to prove our own existence to ourselves, and it cannot be used to prove our existence to others because they cannot ascertain the truth of the premise "I think" in our case. - 2. "would be circular: The thinking thing thinks, therefore it exists" First, this is not circular, only self-evident. Second, this is not the Cogito. Commented Sep 5, 2023 at 15:40

Descartes's "cogito" can be false, because there are conceivable and logically possible situations where there exists thought and no Self.

Below you will find my argument for this contention. It is a paper I wrote for an epistemology class in 2005, entitled "No Cogito". The entire content of the essay is fully copyright protected. Also, some of the formatting was lost copying the text from Word to Markdown, so bare with me and pretend that anything in Latin that isn't in English is in italics.

No Cogito

I. Descartes' Mistake

In “Meditations 1 & 2”, Descartes attempts to reevaluate all of the beliefs that he intuitively holds to be true. His purpose is to discern which beliefs are subject to doubt and which beliefs are necessarily true. Descartes refers to the necessarily true beliefs as “certain” (49). Although the “Meditations” do not offer an explicit definition of certainty, Descartes does describe and imply the characteristics necessary for certainty. For the purposes of this essay, the term certainty describes any proposition where there is no conceivable situation in which the proposition could be false.1

Descartes particularly addresses two different classes of belief: a priori and a posteriori. A priori beliefs include methods of reasoning and thoughts that are “logically independent of experience”2. Descartes’ assessment postulated that a priori beliefs were certain. A posteriori beliefs require a basis on empirical perceptions. They cannot exist independently of experience. Descartes concludes that empirical beliefs are not certain, because he can conceive of situations in which his perception is mistaken by deception or confusion.

Now that I have presented a concise explanation of the basis for Descartes’ reasoning, I can discuss the intended purpose for evaluating his argument. Descartes famous Cogito states, “I think, therefore I am”. This paper will contend that the assertion of the Cogito assumes more than is certain. While a priori knowledge does seem to be capable of determining that there is thought, Descartes’ appears to falter when he postulates the presence of a Self – the “I”. This paper will not argue against the plausibility of the existence of Self or the intuitive belief that there is a Self, but instead will assert that the notion of Self does not possess Cartesian certainty. In other words, there are conceivable and logically possible situations where there is no Self.

II. The Intuitive Value of "Self"

Although this essay argues against calling the existence of Self certain, it is only fair to investigate the reasons for believing that Self is beyond doubt. It seems that people naturally believe in their own personal identity. Therefore, intuition is the primary reason for believing that Self is certain. It doesn’t require much more than introspection and examination of language to determine that any person believes he is an individual. In order to provide an accessible illustration of this intuition, I will personally demonstrate my own intuitive belief in myself. At this moment, it seems to me that I am writing a paper. I am also experiencing thoughts, emotions and sensations. It appears clear to me that I am the one having these experiences and thinking these thoughts. I even use the word “I” when I discuss things, which I believe are happening. So, even though I am being skeptical about the certainty of Self I quite naturally believe that I have personal identity.

There are two significant problems with an inference from an intuitive belief in Self to an assertion of the certainty of Self. The first problem is that intuition does not prove anything more than a prima facie plausibility, and even if a possibility is plausible it does not follow that it is true. For example, the belief that the earth was flat was quite plausible at one time. People saw a flat ground and determined that the earth must be flat. This is obviously not the case, however. Furthermore, I will reiterate that I do not argue that the non-existence of Self is plausible, but possible. The second problem with Descartes’ reliance on intuition is that he has already indirectly disregarded the possibility of intuitions as certain. The belief in “I”, like other intuitive beliefs, rely on empirical perceptions. If I had never experienced the world, I would not be able to distinguish between thing that are internal and things that are external. All things would be the same. This correlates to the notion that our ancestors would not have believed in a flat earth if they had never seen a flat ground. Therefore, the argument against the certainty of Self with respect to intuition is as follows.

  1. Descartes can be deceived about a posteriori beliefs.
  2. If P is an intuitive belief, then P is an a posteriori belief.
  3. The existence of Self is an intuitive belief.
  4. The existence of Self is an a posteriori belief. (2,3)
  5. Descartes can be deceived about the notion of Self. (1,4)

From this, one can plainly see that the existence of Self is not certain. My next step will be to offer examples in which the Self does not exist. This counterexample will further clarify that the existence of Self is not certain.

III. Where the Existence of Self is False

The process of providing a conceivable situation in which there is no Self requires several steps. I will begin by presenting a situation in which someone is confused about the nature of his own Self, and his Self will not in fact be his own. I will then broaden this new notion of Self to a universal, and eventually will entirely abandon the notion of Self. Once this is done, I will defend my counterexample against possible objections and it will thus be proven that the existence of Self is not certain.

To begin I will talk about my friend, Charles. Charles is a very confused and probably insane individual. Charles believes that his foot can think. Though he only has one mind, he unknowingly associates this mind with two different identities: his foot and himself (in the traditional way). So as not to get confused, I will call the traditional mind of Charles by the name Chucky, and the foot-associated mind of Charles by the name Matilda. Matilda has relatively simple thoughts. Whenever Charles puts a sock on, Matilda believes that it is nighttime, and when Charles takes a shower Matilda believes it is raining and wonders why that body to which she is attached won’t give her the Nike raincoat she likes. Chucky is completely unaware of the thoughts that Matilda seems to be having. Likewise, Matilda does not know that she is only an imaginary by-product of Charles’s abnormal psychosis.

In the case of Charles, Matilda believes that she is just like anyone else. She believes that she is an individual and therefore has a Self. However, it is obvious that Matilda is not an individual. Matilda doesn’t even exist. The foot exists because it is a physical part of Charles. The thoughts that Matilda seems to have exist as well, however they are not Matilda’s but Charles’s. It would be ludicrous to think that Charles’s foot is actually having thoughts. Now, one of the beliefs that Matilda had was that she had a Self. This is not the case, because something that does not exist cannot have an existent Self.

The implication of the Charles example is that in the same way Matilda was mistaken about having a Self, Charles could be mistaken about having a Self. Perhaps Charles doesn’t really exist, but his thoughts result from the Godfrey’s mental confusion in the same way that Matilda’s thoughts resulted from Charles’s mental confusion. I would also like to point out that while I did choose to use a physical entity to associate with Matilda, it is not necessary. I did this merely for simplicity and understanding. Matilda could have just as easily not been associated with anything physical at all. So, Descartes did not necessarily have to have a Self in the same way that Matilda did not have a Self, despite the instance of his thoughts. The obvious argument against this contention is that there is still a Self. It may not be of the same nature in which Descartes thought, but all of the confusion does end up being part of someone’s confused Self. Nevertheless, if Matilda were to evoke the Cogito argument it would fail, because by “I think” she would refer to Matilda, not Charles. The next objection is that even if there are some instances in which the Cogito fails, there must be instances in which it succeeds. While I do believe that even with this objection Self is no longer certain, I will strengthen my case by providing an example in which no Self exists.

It is clear that there is something that exists and I will agree with Descartes that this “something” is thought. The task is to conceive of a situation in which there can be a thought with no thinker. I have already given an example in which a thought exists but is associated with a different Self than would be immediately obvious. Let us examine the following conceivable example. There are two people 3: Herman and Gertrude. Herman and Gertrude are not acquainted with each other and might as well live in different continents. The relation between Herman and Gertrude is that they share the same thought-wave sequence. Thought waves work just like sound waves, except much faster. They travel at a rate so fast that they can go from Asian Herman to South American Gertrude and back, without any realization of an instance in which he had no consciousness. These waves are very similar to brain waves in the relationship with Herman and Gertrude, except that they are not limited to existing within one person. Every thought that Herman has is really just a point on the waveform. There is an association of the thought wave with Herman in the same way that thoughts associated with Matilda in the previous example, but it seems that Herman does not have an individual Self.

Now, imagine that these waves do not only comprise the minds of Herman and Gertrude but all of the minds in existence. This would entail that each person’s thoughts do not associate with a Self or personal identity, but actually are a miniscule part of one infinitely extensive waveform. “Where would this wave come from?” one might ask. It might appear that it would still have to emerge from some massive Self, just like Matilda’s thoughts emerged from Charles’s Self. However, it is conceivable that the wave existed without a Self. On a smaller level imagine that a neurologist is able to determine the precise part of the brain that creates brainwaves. He then extracts that piece of the brain from a person and supports its functionality by synthetic means. Now, he has a brain that produces waves and exists independently of any person. A piece of a brain that produces waves would not necessarily have and identity. Even more clear, suppose that this brain’s function is duplicated to a computer. The waves result from something that has no chance whatsoever of being associated with a Self. However these waves do exist. Magnify this example and combine it with the example of the larger scale waveform. What follows is a situation in which every thought of every person in existence is a point on a wave, which originates from a computer. A computer here is something that does not associate with the notion of Self.

This example should prove beyond doubt that the existence of Self is not a certain concept. I foresee the potential for this argument to be presented with two specific objections. First, one might argue against the plausibility of this argument. Suppose that a skeptical reader tells me that he can provide a parallel argument that is extremely implausible. “What if thoughts are really peanuts?” the skeptical reader asks me. “What if every time I have a thought I am encountering a peanut? Surely nothing about seeing a peanut implies self?” I have several things to say about such an example. For starters, there is nothing that would make one think thoughts are peanuts. However, there are real instances in which our perceptions are actually waves; for example, sound. Secondly, I am not arguing for the plausibility of the argument I have presented. My task was merely to prove that I could conceive of a situation in which the proposition that a Self necessarily exists is false. I have done so. And, while it might be extremely absurd to imagine that thoughts are peanuts and hence there is no Self, it is possible to conceive of it. Therefore, such an opposition actually strengthens my argument by offering another counterexample to Descartes. The second opposition that I foresaw was an argument against a necessary premise for my example, which states that the mind associates with something physical (i.e. brainwaves). This argument does not hold much weight as can be seen when the proposed counterargument is more closely examined. I argue that there is no Self in part because the mind is the brain. The counterargument is that the mind is not the brain, because it is actually something else, which is related to a non-physical Self. This unquestionably begs the question, and is therefore not valid.

The argument I have presented makes plain that the existence of Self is not certain by Cartesian standards. Consequently, Descartes’ Cogito has been refuted and can be reduced to the following. There is thought, therefore thought exists. This claim is much less interesting than the Cogito but much more concrete.


  • 1 “The proposition P is certain for S if and only if S cannot conceive of a situation in which it is false that P” – Witmer, Gene. “The First Meditation: A Close Look”. February 4, 2005.
  • 2 A Priori. Oxford American Desk Dictionary and Thesaurus. © 2001 Oxford University Press.
  • 3 To avoid any criticisms that would arise as a result of word choice I feel it is necessary to clarify that by this use of the word “people” I do not imply that each person has a self. What is meant here by “people” is that they have the characteristics that we perceive in people – independently of the question of Self. For all intents and purposes “people” can mean no more than living bodies in this instance.
  • 6
    "The entire content of the essay is fully copyright protected." Note that you've agreed that all your submitted content is licensed under a CC-by-sa license. This reads out loud in the TOS (§3) which you've agreed on upon creating an account. This is just to inform you; if you don't like it, you could summarize the content here and post the fully copyrighted version elsewhere :-) Commented Jun 29, 2011 at 18:07
  • @smartcaveman, I think the point of I in cogito is not the existence of a self, but to point out the first person subjective point of view. You write "there is thought, therefore thought exists", but how do you know for certain there is thought? the "I think" points out the direct witnessing of inner experience.
    – nir
    Commented Aug 5, 2014 at 20:02
  • @smartcaveman The Cogito doesn't assume self. Commented Aug 19, 2019 at 8:58
  • Very interesting. The requirement of brain for existence of mind is the weakest point. Nonetheless highly thought provoking.
    – tejasvi
    Commented Apr 8, 2021 at 15:01

It depends on how You define "thinking" and "being". And You have to define them before going further. But we usually understand them, or think we do, by common reason.

As Wooble said "I" has to exist first, before it can do thinking. But I believe that this sentence means exacly that, that "I" has to exist first ... so this sentence is trying to define what thinking means (that only living beings can think).

But I think Decartes is saying obvious (might not be in his time). From experience I can make these cathegories:

  • one part of living beings can think (humans, dogs ...)
  • other part of living beings can't think (sponges, plankton, ...)
  • non-living beings can't think (rocks), although it depends on how You define thinking because some processes might appear intelligent

From these You can see that if You think then You must be living being (because "can think" is only in statemens with living beings). But as soon as You can claim that some non-living beings can think Decartes statement is false.


Descartes Cogito ergo Sum says quite a number of things:

  1. Descartes was interested in setting a scientific and axiomatic form for philosophy. Hence the axiomatic form of the statement.

  2. We do not doubt we exist - we know we are here now and in the world. But philosophers can take up certain positions and one is of extreme skepticism. Descartes shows that this position is untenable.

  3. The "I" that does the thinking is taken apart by Husserl to a bare phenomenological "I" that is simply perspectively receptive and a psychological "I".


One counter argument to the Descarte's Cogito Ergo Sum is the idea that you do not need to be a thinker to have a thought. This was inconceivable in the 1700s, and is still not wholly convincing now. It rests on the idea that something that is not conscious can exist.

  • 1
    Do you mean conscious or self-conscious? (Can I bring thermostats into the discussion?) A thermostat is conscious of the temperature (that is it has knowledge of the temperature), but is not self-conscious. So "I think..." is self-consciousness.
    – leancz
    Commented Aug 17, 2011 at 7:45
  • 1
    +1 since a computation could be considered a thought and done by a non-thinker and similarly with questions I perceive as thought that could be done by "thinking machines" so the philosopher could be the only thinking being and still there could be other thoughts and ideas than belonging to the philosopher, for instance the opposite of what the philosopher expects can have a real probability and therefore probabilities can be more real than thinking. Commented Aug 17, 2011 at 15:41
  • @leancz I meant conscious, e.g. consciousness, not self-conscious which has different connotations.
    – Chris S
    Commented Aug 17, 2011 at 17:31

Isn't the most logical conclusion that the most certain conclusion you and I can make is that questions exist? I could have made a mistake reasoning somewhere when ruling out that I don't exist and in fact my conclusion that I exist could be wrong. I don't deduce a contradiction from assuming that I don't exist but I do deduce a contradiction from assuming that questions don't exist. If questions don't exist then logic can't exist. Ergo: There are questions that exist with greater certainty than I do.

  • So do you mean that "I doubt, therefore questions exist"? Sounds a little circular or tautological, doesn't it? And who asks the questions?
    – draks ...
    Commented Oct 27, 2015 at 12:14

"I" and "exists", I think are words heavily loaded with baggage. In a simpler age, it wouldn't have been problematic, but in an age where there are so many abstract notions in everyday parlance, as well as due to the efforts of these crazy creatures known as professional philosophers, it's all too problematic.

But I like that even Descartes' neat little answer is problematic... The best answer to skepticism that I'd ever heard was Kierkegaard's. To paraphrase: Doubt is a way of looking. Whilst in that mode, all is doubtful. The answer isn't so much to find an archimedian point (there is none), but to decide to stop doubting.

Philosophy in modernity is in essence a falling away from the ordinary concepts - to step outside it and cast it into doubt. Kierkegaard can be seen as someone preaching religious faith, but it's also an argument against seemingly sophisticated thinking... the sort that makes the learned seem dumber than a five year old.


I think the key to "cogito ergo sum" is to realize that while it is TRUE, it is not something which can EVER be proven, except to the "I" who is making the statement. It is not a circular argument, though it does appear so but rather a most basic one. The "I" necessary to convey the notion of "I think, therefore I am" is immediately present as soon as there is thought; where there is "thought", there is an "I" thinking it. The idea is an instantaneous concept, an understanding, that does not need words until one needs to express it to someone ELSE. You can't have a circular argument if the argument is a point. ;)

  • It's not clear it is true, though. Perhaps society is required to even construct an 'I' capable of thinking Cogito ergo sum. Remember, it says 'thinking' ⇒ 'being'.
    – labreuer
    Commented Feb 23, 2014 at 22:18

If I interpret "I am" to mean "I exist," then the conclusion is false. The reason for this, is that if you don't exist, then thinking or not thinking is not applicable. If you do exist, then it is irrelevant whether you are capable of thinking or not - you already exist!


I think it should be noted that with regard to "we can't truly know anything", there is an answer that is unrelated to 'cogito ergo sum' but yet is perfectly valid.

You can absolutely know at least one thing and this one thing is "I am not omniscient". If you are wrong about this then in fact you know everything and are merely being dishonest, yet if you are not wrong then you do know at least one thing.

As long as one has the capacity to think "I am not omniscient" then it is not sound to claim "we can't be sure we know anything".


The self-aware knower “I am” appearing in consciousness is the 'Person'. People experience themselves as persons. This experience is also of the person as the 'knower'. A 'knower' in the mind, same as the person, is ignored in bio sciences. Life is the source of knower-person in the mind. Mind is consciousness. Knower, person, consciousness and mind are not accepted as primary existential concepts in the sciences. In physics and in bio-sciences the primary focus is on a permanent world of objects outside the mind. This view is the legacy that Descartes gave to the sciences. Starting with the duality of mind and body, the primary nature of the material world which is of the nature of body, was formalized by Descartes. Still, this primary reality or truth is based on false logic. The world is secondary to the knower of the world. But in a democratic brotherhood of scientists, the right of the majority of persons to vote for primacy of matter cannot be denied.

In his 'meditations' Descartes stated that the brain, the body it is in, and the world of objects in which the bodies are, have all been created by God. That world exists independently of its knower and outside the mind. ‘I think, therefore I am (COGITO ERGO SUM)’ was his phrase that downgraded supreme truth "I am" below the thought process called mind which then could be shown to be dependent on the material world as the source of thoughts. Mind was with a knower “I am” in it. Descartes argued it was the first part of a dual reality; the mind and body. They both existed independently and yet, as a duality. The thinking mind does not have a physical extension. The body has an extended presence but does not think. The ‘I’ is distinct from the body and has the ability to exist without the body. But, it can turn to the body by conscious choice. This is how Descartes argued to himself in his meditations to promote body to primacy to which conscious 'I' can turn.

Descartes argued, it may be said that the mind has an existence no less valid than material existence. The mind is called mental phenomena. It is distinct from physical phenomena by quality of abstractness in place of the quality of materiality. The faculty of the mind which is the core of an individual person is located in consciousness. Or mind can be located within the body which is conscious. In the body the mind goes into brain of the body. When current day scientists say brain produces the mind they reduce the dualism of Descartes to monism of matter.

Richard Dawkins wrote “a dualist acknowledges a fundamental distinction between matter and mind. A monist, by contrast, believes that the mind is a manifestation of matter and cannot exist apart from matter. A dualist believes mind is some kind of disembodied spirit….. Like most scientists, I am not a dualist… I have learned to be an intellectual monist….The idea that there is a me,… is deeply ingrained in me and in every other human being, whatever our intellectual pretension to monism.” (Dawkins, 2006)

Instead of material monism, if mind is created by Life, the mind consists of forms in consciousness. Body and other objects are forms in the mind with material quality. They are projected outside the mind and withdrawn, by life in every present moment. The material projections are withdrawn into abstract mental memory at the end of each present moment to make room outside the mind for the projection of the next moment. A new altered world of objects, is the projected in every next present moment, outside the mind.

Descartes did not focus on the logical necessity of keeping the outside of the mind clear. Clearance is necessary so that, only the projected world of objects, of the present moment, exists outside the mind. The experience of all persons is only of the world of the present moment. An object is nothing but objectification of the form created in the mind with attribution of material quality to it. No one perceives past states of the world outside the mind. The past is withdrawn into memory for recall from memory. The knower “I am” in the mind, is the prime truth. The projected world appearing outside the mind in every present moment is secondary truth. This view corresponds as well to the duality formulated by Descartes. The logical necessity to withdraw the projection of every present moment into memory was a third truth which was overlooked by Descartes.

Memory resides in the mind but is correlated to neurons of the brain. Only in the mind can the present moment and the past which is recalled from the memory co-exist. Outside the mind only the present moment exists. This fact is self evident to human beings. Still, the Cartesian illusion of a permanent world outside the mind persists as a logically impossible illusion in physics and in bio sciences. Further, the world is said to be a God created permanent world outside the mind wherein past and present of matter coexist simultaneously. This illogicality was highlighted by mathematician Sir Michael Atiyah.

According to mathematician Sir Michael Atiyah , all physical models since Newton, including quantum mechanics, assume one basic premise. It is that the model enables prediction of the future from full knowledge of the present. Knowledge of the present and also of the past is necessary to predict the future. That requires that memory of the past of the universe comes into the present. For example, velocity of an object is said to be its property in its present state. But, to measure velocity the position of the object ‘now’ must be known and also its position a moment earlier. The knowledge must come from the past moment into the present moment. Otherwise velocity cannot be measured as distance over time. It is in the “knower I am” that the past and the present come together. Mathematics used in physics assumed that knowledge of the present suffices. But, retarded (or delay) differential equations would become necessary to bring data from the past into the present. If we do not have complete knowledge of the past, uncertainty would arise, otherwise.

The agency for an act, as the “doer I am” in the “knower I am” is attributed to a human identity (called a rational agent in Economics). But an agency is not a concept of action in physics. Matter and energy act by themselves according to laws; they are entities altering or acting by themselves. Concept of agency would fall into psychology and not into natural sciences. Past comes into the present in the actions of inanimate objects studied in physics. Its models are based on an illusion ‘of the past in the present’ according to Atiyah.


You mixing concepts. Clear them and you have your answer.

  • I will say that to know is to model something, according to a subjective purpose. If I model a boat by folding paper to play with it (my purpose), I'm creating a model. Models need to be as accurate as a subject needs, models don't need to be perfect. I can say I know a rock pebble, because I saw it, and I know what we refer to when we talk about it. My pebble model is enough to say I know it. A scientist might say I don't know a rock because I don't know its chemical components, and from his point of view, that's correct.
  • We can't truly know anything is true if we consider not a subjective purpose, but an objective (e.g. scientific) purpose. In such case, I cannot say I know a rock pebble, because I just perceive its surface, I don't know all its atoms, I don't know all its interactions, I don't know all its history (its Hawkins' information, or the causal chain that caused it to finish in my hands), etc.

So, if I say "I think, therefore I exist", considering that my models of to think and to exist are enough, yes, cogito ergo sum is true.


Do not fall for the weak-minded idea that you cannot truly know anything. These are people already stuck in their heads -- broken. While Socrates may have said something similar, he was in another universe that was interacting with our Biblical one -- and he simply could not figure it out because of its (relative) alien nature.

There is a reason one can know things. The soul carries a collective history since its beginning. A "genome of experience", you could say. That you can understand what others are saying without thinking about their words is proof of this collective soul. You can even understand them when you don't share the same language because of this shared history. (We did not experience this with the Indians, by the way. They have a different soul.)

The soul grows its "tree of knowledge" from the edges. Most people are stuck in the middle where there is a morass of contradictions which they have never learned to resolve. You have to get above this morass, and until you have your Beginning, you will simply have to trust some smaller truth and continue until you get to the top of the real Truth.


If we cannot truly know anything then science and philosophy are futile. But one thing I can know for sure is that I think. Cogito ergo sum. I think therefore I am. Let's explore the alternative possibilities. I do not think, I have no consciousness. So who is making this statement? I think but I do not exist. Same question. It seems that the only thing that I can reliably know is that I think and consequently I exist. I think that the statement is obviously correct for human beings. I would be interested to see a convincing rebuttal. Is it possible for unthinking beings to exist? Of course. Unless animals, plants and non-living things have some kind of consciousness.

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