Fun times with the Doctor subtilis. From the QQ. super librum Elenchorum, q.1 (Opera Philosophica II, 271-3):
To the question it should be said that logic is of common things as is first philosophy, but in different ways. For first philosophy considers being insofar as it is being, whence it considers a thing according to its quiddity. And because the quiddity of a thing is per se the entity of a thing, therefore first philosophy considers a thing according to its entity. And because it considers a thing according to its quiddity, and many things follow upon a thing according to its quiddity, therefore the first philosopher can consdier the attribute of a subject and about whatever other. For although by understanding being insofar as it is understood in common and inasmuch as it comprehends under itself being of this kind, something cannot be shown, nevetheless many things can be shown about being according to its quiddity; for many things follow a thing according to quiddity, as to be perfect and imperfect, and many others.
Likewise, logic is about common being, or it considers it. But being is double, namely of nature and of reason. Being of nature, insofar as it is such, is the being which does not depend on the soul. But being of reason is said of certain intentions which reason finds in things themselves, such as genus, species, definition, and others of this kind. Being however said in that second way is equated according to its community to being said in the first way. For there is not some being of nature that cannot fall under being of reason, that some intention can be founded over it, as genus or species or property or individual, or at least of cause and caused. Because therefore lgoic is of intentions of this kind, which are applicable to all thihngs, therefore logic is said to proceed from common things.
Further it must be understood that although logic as far as its doctrine is from common things, nevertheless the doctrine handed down in dialectics and demonstration is a diverse use. For dialectic is from common things and in particular sciences argues from common elements to proper conclusions. For it shows that love and hate are receivable in the same thing, not by considering the property of love or hate but this medium that "contraries are made around the same". Whence from common things it does not argue to common, but from common things it argues to proper conclusions. That part of logic which is demonstrative, even if the docrine is handed down from comon things, as for example of a syllogism, nevertheless in special it argues by its proper medium. For the geometer uses the demonstrative art, and thence he receives the first causes of a conclusion, and per a proper medium he argues to a proper conclusion. But one arguing dialectically can show another and another conclusion in another and other science by the same medium. Whence in natural philosophy and medicine there can be shown a diverse conclusion by the same medium.
