  The third version is that “opposite assertions cannot be true at the same time” (Metaph IV 6 1011b13–20). As it stands, this version is neutral about the internal structure of the assertion, but Aristotle assumes that any assertion involves predicating one thing of another. As with the second formulation, one might give a psychologistic interpretation, relating to what people actually do affirm and deny, but the idea that opposite assertions cannot be true at the same time suggests that this third version is better interpreted as a variant of the first formulation.