Wikipedia told me so...

Marshall Poe's 2006 mediation on the online encyclopedia:

The power of the community to decide, of course, asks us to reexamine what we mean when we say that something is "true." We tend to think of truth as something that resides in the world. The fact that two plus two equals four is written in the stars—we merely discovered it. But Wikipedia suggests a different theory of truth. Just think about the way we learn what words mean. Generally speaking, we do so by listening to other people (our parents, first). Since we want to communicate with them (after all, they feed us), we use the words in the same way they do. Wikipedia says judgments of truth and falsehood work the same way. The community decides that two plus two equals four the same way it decides what an apple is: by consensus. Yes, that means that if the community changes its mind and decides that two plus two equals five, then two plus two does equal five. The community isn't likely to do such an absurd or useless thing, but it has the ability.

[via The Daily Dish]