Definition:Logical Formula

Definition
A logical formula, or propositional formula (or, when the context is understood, just formula) is a particular example of a statement form.

The plural of formula is usually given nowadays as formulas, but the Classical plural formulae (or even formulæ) is frequently seen, particularly in older literature.

It is traditional, particularly in the field of mathematical logic, to use lowercase Greek letters to stand for general formulas (the usual ones being $\phi, \psi$ and $\chi$), but more modern treatments are starting to use ordinary lowercase letters of the English alphabet, usually $p, q, r$ etc.