A truth assignment for a propositional vocabulary is a function assigning a truth value to each of the proposition constants of the vocabulary. In this book, we use the digit 1 as a synonym for true and 0 as a synonym for false; and we refer to the value of a constant or expression under a truth assignment i by superscripting the constant or expression with i as the superscript.

The assignment shown below is an example for the case of a propositional vocabulary with just three proposition constants, viz. p, q, and r.