Do you only know that you exist?

Hello. I wrote this to Cecil, but I got an email back suggesting that, since he probably wouldn’t be able to tackle it, that I should post it on the message board. So here it is, in all it’s long, rambling glory. Let me know what you think.

Dear Cecil:

Could you please help settle a gentleman’s disagreement I have with a co-worker? My position (which he disputes) is this: If you really think about it, the only thing you truly know is that you exist. My reasoning starts with Plato’s shadow analogy - that we can’t trust the information about the world we receive through our senses because our senses could be deceiving us (a la the Matrix movies).

My co-worker argues that you know causality is correct, as in “the glass broke because you dropped it.” Bunk says I! How can you test causality if you don’t know whether the glass really exists?

“But what about mathematics?” he replies. “You don’t need the external world to know that 2+2 always equals 4.” Double-bunk says I! Isn’t it possible to dream that 2+2=5? If so, how do you know you’re not just dreaming that 2+2=4 and that, when you wake, the answer will actually be 5?

He then argues that maybe you don’t really exist. It’s possible, I say, but look at my premise: If you think about it, all you know is that you exist. Logically speaking, if I don’t exist, there’s no one to think about the question.

“Aha!” he says. “Since you’re speaking logically, logic must exist!” Bunk-cubed says I! Logic doesn’t “exist” since logic is an activity and not an object. You can’t say you know logic must be correct because, like causality, there’s nothing to test it out on. You can say that you know you are thinking logically, but thinking logically only leads you to the conclusion that you exist (i.e. you’re just saying the same thing with extra words).

He still disagrees, so I ask, can you sort this out, Cecil? Is my premise correct? Or should I just cut back on the weed?

-Your pal Mike

This belongs in Great Debates, not General Questions. Assuming that it will be moved in time, we can proceed to address the o.p.'s question, which is essentially a restatement of the ontological standpoint of solipsism, i.e. that the world exterior to the subject’s immediate experience cannot ever be proven to exist. In an absolute sense, this statement is true–we can’t every prove that everything outside of our immediate vision isn’t just constructed by little blue men right before we glance in that direction–but pointless, because there is no way to test this supposition to falsity. It is also a pretty self-aggrandizing proposition, not only that you are so important that the universe exists specifically for your interests, but all ideas and creations superior to what you can concoct are actually secretly derived from some kind of subconscious (or maybe supraconscious) abilities. If Michelangelo didn’t paint the ceiling of the Sistine Chapel and the ancient Britons didn’t erect Stonehenge, then clearly you must have while you weren’t looking, asbeing the only occupant of this universe.

And so on and so forth; the reasoning gets progressively sillier and more self-absorbed until you end up burrowing into your own navel. So it’s a silly theory, and even moreso if it were actually true, which you cannot ever prove.


Cogito ergo sum, eh? Your thesis is hardly a new idea; it’s just the first two chapters of Descartes’ Meditations on First Philosophy, in pretty much the same order of development even.

As one first objection to the particular position you’ve settled at, let me ask you this: you reject such reasoning as would establish 2 + 2 = 4 because you might only be dreaming that such reasoning is accurate, and will realize some error within it upon awakening. Well, isn’t it equally possible that you are only dreaming that “Logically speaking, if I don’t exist, there’s no one to think about the question.”, and when you wake, you’ll see some fallacy in this reasoning? What’s the distinction between these two cases?

Your premise is called solipsism, the idea that “I alone exist”, and it has been around since at least the time of Gorgias, who lived from 483 to 375 B.C.

Moved to Great Debates.

samclem Moderator, General Questions

The biggest strike against this whole line of reasoning is that it’s supremely uninteresting. It’s the ultimate philosophical dead-end, and there aren’t even any interesting side-trips along the way. Since it’s so utterly pointless, why pursue it at all? Why has anyone wasted their mental effort on this trifling little piece of bunk?

I heard the theory that surprise is a refutation of solipsism. The fact that completely unexpected events occur is evidence that these events did not originate within your own mind and therefore a genuine externality must exist.

But I’ve been surprised in dreams.

I’ve been surprised by programs I’ve written. I know the language and I know my own code, but something interacted with something else in a complex way and surprised me.

It’s in my sex dreams that I most often find myself thinking “Wow, didn’t see that coming.”

I would say that this argument ultimately ends in the conclusion “You can only know that something exists.”

I don’t think you can confidently conclude that you exist. You can detect your own thoughts and must exist to that extent at least, but if you can’t trust your senses to prove that other people exist, you can’t trust them to believe that you have a body or to believe that you perceptions of your internal thoughts are accurate in any way. Perhaps you are just a neuron in a much larger brain with the delusion that the thoughts transmitting through you are yours.

Since the conclusion that something exists isn’t very useful, most people establish some level of faith in the nature of that something. We could call science our system of faith for things that can be objectively measured and tested and religion our system of faith for things that can’t.

That’s the point. If you were just imaging that you were writing a program, then it would work the way you expected it to. At worse, any problems would be the kind of problems you expected to arise. The fact that you find problems that surprise you by being unexpected indicates that the computer has its own reality that exists outside of just your imagination.

Of course, as others have pointed out in their mention of dreams, it may be possible to be surprised by your own mind. The subconscious part of your mind may be able to invent things that the conscious part of your mind doesn’t expect. You’re free to reject the surprise theory as unproven if you wish.

Just to make the distinction clear, the OP isn’t saying that he’s sure that only he exists. He’s saying that the only thing he’s sure of is that he exists.

I believe he is also implying that if other people exist, which he is not really disputing, just not confirming, that they, too, can only be certain that they exist.

First you have to define what you mean by “know.” Once you have established your criteria for knowledge, not just what you can know, but ***how ***you can know . . . only then can you establish knowledge of external reality.

I probably didn’t explain my position as well as I should have , so let me try again. I’m in no way claiming I created cogito ergo sum*. I have only a vague knowledge of Descartes but I’m well aware he came up with this and that there’s no way to truly know whether the external world is real. What I’m arguing is that “I think therefore I am” is the only thing you can truly know. That’s why I brought up the stuff about mathematics, causality, etc… Put another way, do you know anything (logically speaking) other than that you exist?

*: In my defense, however, I am the creator of the First Discount Church of God: the only religion which promises eternal salvation for the low, low price of $9.95.

How do you know it’s bunk? What proof do you have?

Truth need not be interesting, to you, to be true. Solipsism offers the realization that even seeing something with your own eyes may not be enough. It offers the understanding that your perceptions are a world in themselves, and that other people, if they exist, may perceive things differently.

Consider the color blue. Now what if your brain had an odd quirk and blue looked red to you and red looked blue to you. Meaning anything you saw that was red was really blue to everyone else, and blue was really blue to everyone. Swapped just like that.
You’d grow up calling blue red, and red would be blue. You’d never know. You’d live in a universe where the sky was pink, and the phrase “blue bloods” was actually true for everybody, but you’d never know.

That’s the point of solipsism. It’s an exploration of limits of knowing absolute truth.

Edit: crap messed that up.
It should be:

Consider the color blue. Now what if your brain had an odd quirk and blue looked red to you and red looked blue to you. Meaning anything you saw that was red was really blue to everyone else, and blue was really blue to everyone. Swapped just like that.
Could an mod fix it please?

Do you always know when you’re dreaming? Does any surprising thing ever happen in your dreams?

Sure. But then I always get tangled up in my blanket and fall out of bed in the final panel.