A college student was in a philosophy class, where there was a class
discussion about whether or not God exists, The professor had the
following logic:

"Has anyone in this class heard God?" Nobody spoke.

"Has anyone in this class touched God?" Again, nobody spoke.

"Has anyone in this class seen God?" When nobody spoke for
the third time, he simply stated, "Then there is no God."

The student did not like the sound of this at all, and asked for permission
to speak. The professor granted it, and the student stood up and asked
the following questions of his classmates:

"Has anyone in this class heard our professor's brain?"
Silence.

"Has anyone in this class touched our professor's brain?"
Absolute silence.

"Has anyone in this class seen our professor's brain?" When
nobody in the class dared to speak, the student concluded, "Then,
according to our professor's logic, it must be true that our professor
has no brain!"

The student received an "A" in the class.