On the Natural Faculties (1.3)

It appears to me, then, that the vein, as well as each of the other parts, functions in such and such a way according to the manner in which the four qualities [*]

are mixed. There are, however, a considerable number of not undistinguished men — philosophers and physicians — who refer action to the Warm and the Cold, and who subordinate to these, as passive, the Dry and the Moist; Aristotle, in fact, was the first who attempted to bring back the causes of the various special activities to these principles, and he was followed later by the Stoic school. These latter, of course, could logically make active principles of the Warm and Cold, since they refer the change of the elements themselves into one another to certain diffusions and condensations [*]. This does not hold of Aristotle, however; seeing that he employed the four qualities to explain the genesis of the elements, he ought properly to have also referred the causes of all the special activities to these. How is it that he uses the four qualities in his book On Genesis and Destruction, whilst in his Meteorology, his Problems, and many other works he uses the uses the two only? Of course, if anyone were to maintain that in the case of animals and plants the Warm and Cold are more active, the Dry and Moist less so, he might perhaps have even Hippocrates on his side; but if he were to say that this happens in all cases, he would, I imagine, lack support, not merely from Hippocrates, but even from Aristotle himself — if, at least, Aristotle chose to remember what he himself taught us in his work On Genesis and Destruction, not as a matter of simple statement, but with an accompanying demonstration. I have, however, also investigated these questions, in so far as they are of value to a physician, in my work On Temperaments.