Mathematical statement that includes one or more variables and is true for some values attributed to these variables and false in other cases.

The defined set of variables of a propositional form is called the universal set of this propositional form.

- An expression like 3
*x*– 5 = 7 is a propositional form called an equation. - An expression like 3
*x*– 5 is not a propositional form.

### Example

Consider the statement 4*x* + 1 = 9 This equality, in itself, is neither true nor false. If we define the variable *x* in the universal set of whole numbers, this propositional form becomes a true proposition when *x* = 2 and false in all other cases.