Two builders, Fred and Bill, are seated either side of a table in a rough pub when a well-dressed man enters, orders a beer and sits on a stool at the bar.
The two builders start to speculate about the occupation of the 'suit'.

Fred: "I reckon he's an accountant."
Bill: "No way! He's a stockbroker."
Fred: "He's no stockbroker! A stockbroker wouldn't come in here!"

The argument repeats itself for some time until the volume of beer gets the better of Fred and he makes for the toilet. On entering the toilet he  sees that the 'suit' is standing at a urinal.
Curiosity and several jugs get the better of the builder...

Fred: "Scuse me...no offence meant, but me and me mate were wondering what you do for a living?"

Suit: "No offence taken! I'm a Logical Scientist by profession" 

Fred: "Oh! What's that then?"

Suit: "I'll try to explain by example....do you have a goldfish at home?"

Fred: "Er...mmm...well yeah, I do as it happens!" 

Suit: "Well, it's logical to follow that you keep it in a bowl or in a pond. Which is it?"

Fred: "It's in a pond."

Suit: "Well, then it's reasonable to suppose that you have a large garden."

Fred: "As it happens, yes I have got a big garden." 

Suit: "Well then It's logical to assume that in this town that if you have a large garden that you have a large house."

Fred: "As it happens I've got a five bedroom house...built it myself."

Suit: "Well, given that you've built a five bedroom house it is logical to assume that you haven't built it just for yourself and that you are quite probably married."

Fred: "Yes, I am married, I live with my wife and three children!"

Suit: "Well then it is logical to assume that you are sexually active with your wife."

Fred: "Yep! Four nights a week!"

Suit: "Well then it is logical to suggest that you do not masturbate very often."

Fred: "Me? Never!"

Suit: "Well there you are, that's logical science at work!"

Fred: "How's that then?"

Suit: "Well from finding out that you had a goldfish, I've told you about the size of garden you have, the size of house, your family and about your sex life!"

Fred: "I see. That's pretty impressive...thanks mate!"

They both leave the toilet and Fred returns to his mate.

Bill: "I see the suit was in there, did you ask him what he did?

Fred: "Yep! He's a logical scientist!"
Bill: "What's that then?"

Fred: "I'll try to explain. Do you have a goldfish?"

Bill: "Nope"