Propositional form X is consistent with propositional form Y (i.e., X and Y are consistent [with one another]) iff it is possible for both X and Y to be true.
Example from everyday life: 'x is not taller than y' is consistent with 'y is not taller than x'
Example from categorical logic: 'Some S are P' is consistent with 'Some S are not P'
Example from propositional logic: 'p' is consistent with 'p ≡ q'
Example from predicate logic: '(x)Øx' is consistent with '(Ǝx)Øx'
