Philosophy What philosophers do
Philosophers use logic to solve problems and answer questions. Logical consistency is a cornerstone of any acceptable theory. Philosophers who disagree with a theory will often try to find a logical  contradiction within the theory. If they can find one, this gives them a reason to reject that theory. If they cannot find any inconsistency, the philosopher might try to show that the theory leads to a conclusion which is either unacceptable or ridiculous. This second approach is usually called reductio ad absurdum.