identical) with unity in number, for each is a principle. Wherefore by assigning the common genus in all things, we shall appear not to define in a manner foreign (from the subject), and indeed almost those who define, are accustomed thus to explain, for they say that unity is the principle of number, and that a point is the principle of a line; it is evident then that they refer the genus of both to what is common.
The instruments therefore by which syllogisms are constructed, are these; but the places, for which what we have said, is useful, are those (which follow).
Of problems, some are universal but others particular, the universal then, as that all pleasure is good, and that no pleasure is good, but the particular, as that a certain pleasure is good, and a certain pleasure is not good. To both genera, however, of problems, those things are common which universally construct and subvert, for having shown that a thing is present with every, we shall also have proved that it is present with a certain individual, and in like manner, if we have shown that it is present with no individual, we shall also have proved it not present with every. We must first speak, then, of those which are universally subversive, both because such are common to universal and particular (problems), and because men rather introduce theses in the affirmative than in the negative, but the disputants subvert them. Nevertheless, it is most difficult to convert an appropriate appellation (derived) from accident, for (to be inherent) partly, and not universally, it is possible to accidents only, since it is necessary to convert from definition, property, and genus, as if it is