Universa Philosophia

=== LATIN Unde liquido constat cur contrariae non possint simul esse verae, et possint esse simul falsae, subcontrariae autem possint esse simul verae, non tamen simul falsae; contradictoriae autem nec simul verae, nec simul falsae, sed altera vera, altera falsa, quia idem affirmari, et negari simul de eodem vere, repugnat, quia sicut Petrus non potest simul currere, et non currere, quia opponuntur immediate, ita non potest utrumque vere aut affirmari, aut negari. Haec autem est ratio a priori, et unicum fundamentum, cui innititur tota doctrina de oppositione propositionis. === ENGLISH Hence it is plainly evident why contraries cannot be at once true and can be at once false, while subcontraries can be at once true, yet not at once false; but contradictories neither at once true nor at once false, but the one true and the other false, because it is repugnant that the same be at once truly affirmed and denied of the same, because just as Peter cannot at once currere, et non currere, because they are immediately opposed, so neither can both be truly either affirmed or denied. But this is the a priori reason and the sole foundation on which the whole doctrine of the opposition of propositions rests.