LOGICAL

.DAY

Identity

A thing is identical to itself.

Non-Contradiction

Nothing can both be and not be.

Excluded Middle

Every proposition is true or false.

Modus Ponens

If P then Q; P; therefore Q.

Modus Tollens

If P then Q; not Q; therefore not P.

Syllogism

From two premises, a conclusion follows.

Contraposition

If P then Q equals if not Q then not P.

De Morgan

Not (A and B) equals (not A) or (not B).

Biconditional

P if and only if Q; they share truth.

∴

logical.day