When a thing is in potentiality to some further perfection, it is only by accident that it does not attain it. If it were incapacitated for that perfection essentially, it would not be in potentiality at all. An undergraduate, radically and essentially debarred from taking his degrees, would not be an undergraduate. If he is too stupid to take it, that is an accident. Stupidity is not of the essence of his condition.

Of God and His Creatures: 3.7