The Philosophy Exam

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.

Weeks 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?"