Ancient Greek philosophers first described deductive reasoning. One of them was Aristotle, according to which deductive reasoning is a process of reasoning from the general to the specific, and it is supported by a deductive logic. A deductive logic is that according to which for every general claim or action there is an opposite and equal claim or action. For example, from the general claim that all ravens are black birds, the opposite and equal claim is that this bird is a raven and therefore is black.