Even as he said it, he knew he was contradicting himself.
A dissolved in B and B dissolved in A, since both of these solutions emit vapours of the same composition (this follows since the same vapour must be in equilibrium with both solutions, for if it were not so a cyclic system contradicting the second law of thermodynamics would be realizable).
Diogenes (q.v.) began by insisting on the necessity of there being only one principle of things, herein contradicting the pluralism of Heraclitus.
The risen Jesus was not as he was, thus apparently contradicting the gospels.
Aquarius is a complex creature with many contradicting ideals and beliefs, at least to the observer.