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Deduction is one of the two main types of reasoning. The other is induction. In deduction, we apply a general rule to a particular case.
Deductive arguments are attempts to show that a conclusion must follow from a set of premises or hypotheses. A deductive argument is valid if the conclusion follows necessarily from the premises.
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".
