Deductive reasoning |

Deductive reasoning, also deductive logic or logical deduction or, informally, "top-down" logic,^[1] is the process of reasoning from one or more general statements (premises) to reach a logically certain conclusion.^[2]

Deductive reasoning links premises with conclusions. If all premises are true, the terms are clear, and the rules of deductive logic are followed, then the conclusion reached is necessarily true.

Deductive reasoning (top-down logic) contrasts with inductive reasoning (bottom-up logic) in the following way: In deductive reasoning, a conclusion is reached from general statements, but in inductive reasoning the conclusion is reached from specific examples. (Note, however, that the inductive reasoning mentioned here is not the same as induction used in mathematical proofs - mathematical induction is actually a form of deductive reasoning.)



An example of a deductive argument:

1. All men are mortal.
2. Aristotle is a man.
3. Therefore, Aristotle is mortal.

The first premise states that all objects classified as "men" have the attribute "mortal". The second premise states that "Aristotle" is classified as a "man" – a member of the set "men". The conclusion then states that "Aristotle" must be "mortal" because he inherits this attribute from his classification as a "man".

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