Nonexistence is sometimes mentioned in discussions of the meaning, or analyzability, of "existence." It is frequently pointed out on this topic that there are a variety of senses in which something can fail to exist (see the following list, as just an example). Some philosophers have suggested that "exists" has only a "negative" meaning: while we cannot say what it means for something to exist, we can say what we mean when we say that something does not exist. For example:

  • In fiction: Romeo and Juliet do not really exist, because they are merely characters in a play. So there is fictional nonexistence.
  • Suppose one is just daydreaming and one imagines winning the Nobel Prize. This Nobel Prize does not exist: it is just imaginary. So another kind of nonexistence is imaginary nonexistence. (Or one might say, tendentiously but idiomatically, "It has existence only in one's imagination.")
  • Consider that old hypothesis, that the Earth is flat. People who thought the Earth was flat thought there was an edge to the world, and if one sailed too far across the ocean one would sail off the edge of the world. The world is not flat but roughly spherical, and the edge of the world does not exist. So that is a another kind of nonexistence: hypothetical nonexistence. In other words, that is the sort of nonexistence that false posits have, when one posits something in a false hypothesis.
  • legendary (Loch Ness Monster)
  • mistakenly inferred (the aether)
  • There is a quite different kind of nonexistence, namely, the kind the ancient Greek philosopher Socrates now has. Socrates does not exist now. We think he did exist, but there is a sense in which he does not exist; namely, he does not exist any longer. So another sort of nonexistence is present nonexistence. The person who will be President of the United States 200 years from now does not currently exist (and may never exist). So we might distinguish two types of present nonexistence--the sort had by entities that supposedly did exist and the sort had by entities that may exist in the future. Another interpretation of reality is that all things (,events, etc.) that ever exist actually always exist. This is closely related to the idea that all possible worlds exist. The many-worlds interpretation of quantum mechanics and alternate universes are related concepts.

The multiplicity of ways in which a thing can fail to exist has been so striking to some that it has been suggested that existence is, in fact, merely an "excluder" concept--used to classify items by what they are not (not fictional, not imaginary, not mistakenly inferred, etc.)--as 'real' is sometimes thought to be.

One central problem that philosophers face in thinking about nonexistence is generally discussed under the heading fictional truth. How can we account for the truth of the proposition 'Romeo killed himself' when Romeo is nonexistent? (This one is easy. Consider it false.)

The significance of these distinctions may be inferred from the following:

"Everyone knows that dragons don't exist. But while this simplistic formulation may satisfy the layman, it does not suffice for the scientific mind. The School of Higher Neantical Nillity is in fact wholly unconcerned with what does exist. Indeed, the banality of existence has been so amply demonstrated, there is no need for us to discuss it any further here. The brilliant Cerebron, attacking the problem analytically, discovered three distinct kinds of dragon: the mythical, the chimerical, and the purely hypothetical. They were all, one might say, nonexistent, but each nonexisted in an entirely different way...."
-- Stanislaw Lem, "Cyberiad"

See the existence of physical objects.