Propositional form X is self-contradictory (i.e., X is a self-contradiction) iff it is impossible for X to be true. In other words, X is necessarily false.
Example from everyday life: 'x is a bachelor and x is female'
Example from categorical logic: 'No S are S'
Example from propositional logic: 'p • ~p'
Example from predicate logic: '(x)(Øx ﬤ ~Øx)'
