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.