If this is two

If this is two ... is a prominent riddle. The solution is quite easy, but can you find it just by listening to examples of correct answers?

Equipment
You don't need any equipment for this riddle.

Procedure
The trainer - or somebody else who knows the correct solution - ask several questions:
 * He raises his right hand, and presents any number of fingers (zero to five). [let's call this number A]
 * Additionally, he claims: "if this is [any number], ..." [this number is B]
 * Then, he shows another number of fingers [number C]
 * And says "... then this is [number D]".

Usually, he for all four numbers, values between zero and five are valid (unless you got more fingers :-) )

All the participants have to guess, what the correct number D is (depending on A, B, and C). So, usually, after a few initial rounds, the trainer does not tell the number D, but instead asks "what would then be that?".

Trivia

 * The game is used in the computer adventure Monkey Island 2: LeChuck’s Revenge.

Solution
If you are to lazy to find the solution by yourself, you can find it here: if this is two/solution

Wenn das zwei ist