The fish bowl argument is the observation that things are the way they are not due to some improbable (or otherwise) happenstance but rather because we are completely unfamiliar with the alternative. The classic example is two fish in a fish bowl who will never know that there is any sort of a world whatsoever outside of their small glass bowl because they've never seen it. As far as they are concerned, the fish bowl is their reality. If fish could talk, and you asked those fish to describe what the word "dry" means, assuming the fish haven't had any traumatic experiences, they wouldn't begin to understand because they've spent their whole lives wet.

Applying that to the universe, we say "Why do we exist?" and of course the trivial fish bowl argument response to that question is "If we didn't exist, we wouldn't be here to question if we exist."

This leaves me to question if we really know what nonexistence means. For example, can we truly imagine a color which has never existed? Are we really capable of determining if something exists or not, since we've never actually placed eyes on something which doesn't exist? You could argue that you can imagine an elephant with wings and since such animals don't exist that one can determine what exists and what doesn't, though it's not true that it doesn't exist necessarily. On some planet in a galaxy far away, perhaps there exist elephant-like creatures with wings. I could go so far as to argue that if the universe is infinite, it isn't possible that something does not exist (assuming of course the very definition itself isn't contradictory like a triangle with four sides).

Therefore I can only conclude that we can only determine what exists. We cannot determine what does not exist on this basis. We know that the set of things which do not exist is everything which is not contained in the set of things which do exist, by definition of existence, though we cannot determine its characteristics. We cannot even determine if the set of things which do not exist is empty or not.

I know this might seem like an odd question, but let me just say that I'm not chomping on cheetos and smoking mary jane. Is this logic sound or perhaps trivially so, or am I missing something?

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    You are not asking a question, you are arguing a point. It happens to be correct, but this is still not a question. See also: books.google.com/books/about/… Commented Jun 29, 2011 at 13:05
  • I am asking for anyone's take on my point. Would it have been any better had I asked "Do we exist?" I don't think it would have been.
    – Neil
    Commented Jun 29, 2011 at 13:29
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    No, I think "Is it possible to determine an object's nonexistence?" is a valid question. You however do not ask it, you answer it. Commented Jun 29, 2011 at 13:31
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    Strangely I find my self in agreement with Lennart on this one.
    – Chad
    Commented Jun 29, 2011 at 13:48
  • @Neil: I agree with Lennart that this is a perfectly valid question, but the way it's phrased makes it sound like an argument instead. It's been brought to my attention as a candidate for re-opening, and I want to agree, but it's not really phrased like a question. Please consider extracting your answer/opinions out of the question proper and later posting them as an answer (yes, you can answer your own questions). Keep in mind that, in general, we want to encourage answers that are thoughtful and comprehensive rather than simply "Yeah, you've got it about right". Commented Jul 3, 2011 at 13:57

4 Answers 4


Kant famously argued that existence is not a predicate in his analysis of the ontological argument for the existence of god.

Kant argues that "'being' is obviously not a real predicate" and cannot be part of the concept of something. That is, to say that something is or exists is not to say something about a concept, but rather indicates that there is an object that corresponds to the concept, and "the object, as it actually exists, is not analytically contained in my concept, but is added to my concept". For objects of the senses, to say that something exists means not that it has an additional property that is part of its concept but rather that it is to be found outside of thought and that we have an empirical perception of it in space and time. A really existing thing does not have any properties that could be predicated of it that differentiate it from the concept of that thing. What differentiates it is that we actually experience it: for example, it has shape, a specifiable location, and duration. To give an example of Kant's point: the reason we say that horses exist and unicorns do not is not that the concept of horse has the property of existence and the concept of unicorn does not, or that the concept of horse has more of that property than the concept of unicorn. There is no difference between the two concepts in this regard. And there is no difference between the concept of a horse and the concept of a really existing horse: the concepts are identical. The reason we say that horses exist is simply that we have spatio-temporal experience of them: there are objects corresponding to the concept. So any demonstration of the existence of anything, including God, that relies on predicating a property (in this case existence) of that thing is fallacious. (wikipedia)

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    Interesting argument Kant made. Existence of God cannot be treated as a property of the concept, as the concept of an object, regardless of whether it exists or not, is the same in either case. Moreso, nothing can be argued about a non-existing object since it cannot be proven to be so.
    – Neil
    Commented Jun 30, 2011 at 15:06
  • The debate is more subtle than that and Kant argument is hardly an up-to-date account of debate. The question of negative singular existential statements are one of the central problems in philosophy of language and metaphysics. See this plato.stanford.edu/entries/nonexistent-objects
    – Arash
    Commented Sep 27, 2013 at 12:49

In mathematics, it is certainly possible to prove that certain things do not exist. For example, if your "fishbowl" is the integers, i.e. the whole numbers, then you can answer "no" to the question "Is there a square root of 2?" and be completely certain in your response. Of course, if you enlarge your fishbowl to include all real numbers, then suddenly a square root of 2 does exist (two of them, in fact).

There are also less trivial examples. A familiar one might be the statement "There does not exist a triple (x,y,z) of integers such that x^n + y^n = z^n when n is bigger than 2" which is commonly known as Fermat's Last Theorem. This theorem is true, and firmly establishes the nonexistence of an entire set of triples (a,b,c) with a given property.

Of course, mathematics relies upon a certain (small) set of axioms, and it's always possible that changing your axioms makes things pop into existence. But once you've set your axioms/fishbowl, it is certainly possible to say definitively that things do not exist.

I suppose the question then becomes: is it reasonable to ask questions about the existence of things outside of our fishbowl? That might be your real question. As for that...I would say "no", but it seems to be more a matter of opinion than anything else.

  • I think that's a different definition of the word "exist." By exist you mean "defined". It's all abstract and nothing in mathematics exists in a physical manner. It'd be like debating whether or not love exists and can be measured. On the contrary I'm referring to anything which has the potential of existing. Everything else is trivially false.
    – Neil
    Commented Jul 4, 2011 at 10:21
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    I'm not so sure about that. Consider the halting problem. At least to me, the non-existence of a machine which can solve the halting problem does not seem to be based on physical obstructions -- that is, if we could theoretically build a machine that could analyze any computer program and determine if it could halt, it is not clear to me that we would not also be able to build it. Of course, the argument "If we could build it, then we could build it" is sort of ridiculous, but I think (hope?) my point is clear.
    – Jeff
    Commented Jul 7, 2011 at 14:24

You can tell that an object doesn't exist if descriptions of its properties are inconsistent. If a concept doesn't have an existing instance, there's no experiential way to show that, so an analytic way must be used if possible.

  • How do you mean by inconsistent? A four-sided triangle? That's trivially true. Objects which cannot logically exist don't actually exist. And so?
    – Neil
    Commented Jun 30, 2011 at 14:53
  • To determine if something exists, you have to find something, then test to see if it has the properties desired. To determine if something does not exist, you can't use this method (it doesn't exist so you can't produce it to test it). But you do have the properties and you can check that the properties are -inconsistent-, then you know it cannot exist. You might be discounting that as trivial, but it is one way to prove nonexistence.
    – Mitch
    Commented Jun 30, 2011 at 16:13
  • ...To check if some set of consistent (that is, possible) properties has existing examples, you'd have to enumerate 'everything', test each one, and get 'no' each time. This is doable mathematically (where infinite sets are manipulable in a finite operation), but not in real life, where we only have a finite amount of time to do things, and so far the world seems infinite.
    – Mitch
    Commented Jun 30, 2011 at 16:14
  • Testing every possible object is not a good way to prove that something does not exist, even in mathematics. See my answer.
    – Jeff
    Commented Jun 30, 2011 at 21:08
  • @Jeff: I think my point was that, whether confined to mathematics or not, enumeration of all objects is impossible (and so you can't prove nonexistence by enumeration) but one can test all elements an infinite set without exhaustive enumeration (via common properties or induction) to prove that none satisfy a property.
    – Mitch
    Commented Jun 30, 2011 at 22:26

I think this depends on how you define existance. Even if you are nothing more and a creation of my mind then you exist even if it is just as that creation in my mind so long as I continue to think of you and/or have a memory of you.

Existance as we know it can only be defined through the interpretations of feedback of our nerves by the synapes and neuron in our brain. I only know this because scientists have determined this however it is possible that my mind created this knowledge. It is also possible that we (or at least I) exist as something that has my thoughts and interpretations but is not designed or allowed to comprehend actual existance (Think living in the Matrix. They exist as their bodies in the matrix but also have actual bodies outside the matrix.)

I can concieve of no way to disprove an actual existance that does not result in the destruction of the percieved existance.

  • You named a perfectly good example. Although the bodies in the matrix are the "same" as our perceived bodies, it doesn't necessarily have to be the case, yet we still have a perceived existence of our bodies in the matrix.
    – Neil
    Commented Jun 30, 2011 at 14:51
  • The thing is you could argue that the existance is the matrix is part of the actual existance.
    – Chad
    Commented Jun 30, 2011 at 17:00
  • Now you're suggesting that anything I could 'construct' in a computer program could exist if it could be experienced as a typical object could.
    – Neil
    Commented Jul 1, 2011 at 10:08
  • Actually I am saying that it does exist even if only as bits in the computer(Assumimg that the computer exists). And that Our perception of existance is not neccessarily correlated with any actual existance. A great example of this would be a mirage. (we think)Our brain takes little pieces of information and intreprets them and fills in missing pieces. The mirage doesnt exist and our brain destroys the percieved existance as soon as it recognizes that it is not there.
    – Chad
    Commented Jul 1, 2011 at 12:26

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