Logic puzzles
Paradoxes
Simply put, a logical paradox is a sentence, statement, or argument that contradicts itself. A well-known example of a paradox is the following sentence:
This is a false statement.
If the statement is true, it is false, but if it is false, then it is true?!
Another famous paradox is the ‘barber’s paradox’.
A barber is known to shave all the men in the city who do not shave themselves. Who then, shaves the barber?
Smullyan’s knights and knaves puzzles
Smullyan has greatly enriched the field of logic puzzles. His favorite puzzles are tales of “knights” (people that always tell the truth) and “knaves” (people that always lie).
If the visitor is in the “knights” city, then a “knight” will answer YES, and a “knave” (visiting there) will also answer YES. On the other hand, if the visitor is in the “knaves” city, both a “knight” and a “knave” will answer NO. So, if the reply is YES, he is in the “knights” city, and if the reply is NO, then is in the “knaves” city.
Answering logic puzzles can be pretty puzzling. A good trick is to realize that there are some statements that a liar cannot possibly make, for example, “I am a liar”. These are the sort of statements that we look for so that we can distinguish between liars and truth tellers.