For it must be either homonymously that we say these are, or by making qualifications and abstractions (in the way in which that which is not known may be said to be known), the truth being that we use the word neither homonymously nor in the same sense, but just as we apply the word 'medical' when there is a reference to one and the same thing, not meaning one and the same thing, nor yet speaking homonymously; for a patient and an operation and an instrument are called medical neither homonymously nor in virtue of one thing, but with reference to one thing.