We here speak of the peculiar province of the Commentator; for undoubtedly, in many instances, a commentary on a received author has been made the vehicle of conveying systems and doctrines entirely different from those of the author himself; as, for instance, when the New Platonists wrote, taking Plato for their text. The labors of learned men in the stationary period, which came under this description, belong to another class. 3. _Greek Commentators on Aristotle._--The commentators or disciples of the great philosophers did not assume at once their servile character. At first their object was to supply and correct, as well as to explain their teacher. Thus among the earlier commentators of Aristotle, Theophrastus invented five moods of syllogism in the first figure, in addition to the four invented by Aristotle, and stated with additional accuracy the rules of hypothetical syllogisms. He also not only collected much information concerning animals, and natural events, which Aristotle had omitted, but often differed with his master; as, for instance, concerning the saltness of the sea: this, which the Stagirite attributed to the effect of the evaporation produced by the sun's rays, was ascribed by Theophrastus to beds of salt at the bottom. Porphyry,[24\4] who flourished in the third century, wrote a book on the _Predicables_, which was found to be so suitable a complement {206} to the _Predicaments_ or Categories of Aristotle, that it was usually prefixed to that treatise; and the two have been used as an elementary work together, up to modern times. The Predicables are the five steps which the gradations of generality and particularity introduce;--_genus_, _species_, _difference_, _individual_, _accident_:--the Categories are the ten heads under which assertions or predications may be arranged:--_substance_, _quantity_, _relation_, _quality_, _place_, _time_, _position_, _habit_, _action_, _passion_. [Note 24\4: Buhle, Arist. i. 284.]