benefit enemies, and to injure friends, are contrary to benefiting friends, and similarly to each of the others, there will appear two contraries, to those who consider them after the same manner, nevertheless, whichever contrary is useful to the thesis should be assumed.
Moreover, if any thing is contrary to accident, we must see whether it is present with what the accident is said to be present with; for if this is present, that cannot be, since contraries cannot possibly be at the same time with the same thing.
Also whether such a thing has been predicated of any, which existing, contraries must necessarily be inherent; thus if any one said that ideas are in us, for it will happen that they will both be moved and be at rest; also be both sensible and intelligible. For ideas, to those who admit their existence, appear to rest, and to be intelligible; but if they are in us, they cannot be immovable, for since we are moved, it is necessary that all things in us should be moved together with us, it is also clear that they are sensible if they are in us, for through the sense of sight we know the form which is in every thing.
Again, if accident is laid down to which there is a certain contrary, we must consider whether it is also susceptible of the contrary which contains the accident, for the same thing is capable of contraries; thus if any one said that hatred followed anger, hatred would be in the irascible (part of the soul), for anger is there. We must
