Two guys meet in a bar after work and are discussing what "logic" is.

Neither of them know.

One of them leaves.

A professor walks in and the bartender says, "I bet he'll know."

They ask the professor, who says, "The easiest way to show you what logic means is to give you an example.
Do you have a dog?"

Guy: Yes.

Prof: Well, logic tells me that if you have a dog, you must have a back yard.

Guy: That's right!

P: Logic tells me that if you have a dog and a backyard, the yard must have a fence around it.

G: Right again.

P: Logic tells me that if you have a dog, a yard and a fence, you must have a dog-house in the yard.

G: I sure do!

P: Logic tells me that if you have a dog, a yard, a fence and a dog-house then you must be a heterosexual, married male with children.

G: That's astounding!

P: That's the way logic works.

The two guys meet in the bar the next night after work.

Guy #1: Did you find out what logic is?

Guy #2: Sure.
Let me give you an example.
Do you have a dog?

Guy #1: No.
(Pause)

Guy #2: Logic tells me that you're a goddamn queer!