Philosophy Class

An eccentric philosophy professor gave a one question final exam after
a semester dealing with a broad array of topics. The class was already
seated and ready to go when the professor picked up his chair, plopped
it on top of his desk and wrote on the board:

"Using everything we have learned this semester, prove that this chair
does not exist." Fingers flew, erasers erased, notebooks were filled
in furious fashion. Some students wrote over 30 pages in one hour
attempting to refute the existence of the chair. One member of the
class however, was up and finished in less than a minute.

A week later when the grades were posted, the rest of the group
wondered how he could have gotten an "A" when he had barely written
anything at all.

His answer consisted of two words: "What chair?"