Propositional form X is self-consistent (i.e., X is a self-consistent propositional form) iff it is possible for X to be true. In other words, X is not necessarily false.
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'
