Logical Terms

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Types of Inferences

A line of reasoning from the general to the specific. If you know that all men are mortal and Socrates is a man then you can deduce that Socrates is also mortal.
A line of reasoning from the specific to the general. If you see men growing old and dying then you can induce that all men are mortal.

Both induction and deduction are based on the law of identity.


A tautology is a sentence which repeats the same information. For example:

The law of identity dictates that all truths must ultimately be tautological, although some tautologies can be false. All three axioms are explicitly tautological.