Deductive reasoning is a logical process in which a conclusion is based on the concordance of multiple premises that are generally assumed to be true. Deductive reasoning is sometimes referred to as top-down logic. Its counterpart, inductive reasoning, is sometimes referred to as bottom-up logic. While deductive reasoning proceeds from general premises to a specific conclusion, inductive reasoning proceeds from specific premises to a general conclusion.
Aristotle and deductive reasoning
The Greek philosopher Aristotle, who is considered the father of deductive reasoning, wrote the following classic example:
- All men are mortal.
- Socrates is a man.
- Therefore, Socrates is mortal.
Aristotle’s example is called a syllogism. A syllogism uses deductive reasoning to arrive at a conclusion that is based on two or more propositions that are assumed to be true. The premises of Aristotle's logical argument -- that all men are mortal and that Socrates is a man -- are self-evidently true. Because the premises establish that Socrates is an individual in a group whose members are all mortal, the inescapable conclusion is that Socrates must likewise be mortal.