Aristotle, the first person we know who wrote down laws of deduction, gives this example of deduction:
- All men are mortal.
- Socrates is a man.
- Therefore, Socrates is a mortal.
The first two statements are called "premises". The last statement is called the "conclusion". The conclusion is taken from the premises.
- If the conclusion is wrong, then at least one of the premises is wrong
- If one of the premises is wrong, the conclusion may also be wrong.
Deductive reasoning is often called "top-down logic", whereas inductive reasoning is called "bottom-up reasoning".