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An entity is identical to itself. Usage: Basic principle used in all forms of logic and argument, denoted as $A = A$.

If a given implication is true and its consequent is not true, then the antecedent is also not true. Usage: It is a valid form of argument, denoted as if $A \rightarrow B$ and $\neg B$, then $\neg A$.

For any proposition, either that proposition is true, or its negation is true. Usage: Underlies the principle of bivalence in classical logic, denoted as $A \lor \neg A$.

A statement cannot be both true and false at the same time in the same respect. Usage: Foundational to avoiding paradoxes in formal logic, often expressed as $(A \land \neg A)$ is always false.