Propositional form X is contingent (i.e., X is a contingent propositional form) iff (1) it is possible for X to be true and (2) it is possible for X to be false. In other words, X is neither necessarily false nor necessarily true.
Example from everyday life: 'x is taller than y'
Example from categorical logic: 'Some S are P'
Example from propositional logic: '(p ﬤ q) ﬤ p'
Example from predicate logic: '(x)Øx'
