2. For setting down first the genus, then the species, we subjoin also other things that are possibly related, and by setting aside common qualities we make distinctions, continually interposing differences until we arrive at the proper quality of that which we are examining, its meaning being made definite, as, for example: _Homo est animal rationale, mortale, terrenum, bipes, risus capax_. 3. When the genus _animal_ is mentioned the substance of man is declared. For with reference to man the genus is animal; but since it has a wide application, the species, _terrenum_, is added and now what belongs to the air or water is excluded. And a difference is added, as, for example, _bipes_, which is given on account of the animals that go on several feet. Likewise _rationale_, because of the animals which lack reason; and _mortale_, because man is not an angel. 4. Afterwards, when the common qualities had been set aside, the property was added at the end, for it is the characteristic of man alone to laugh. In this way the complete definition to indicate man was reached. Aristotle and Tully held that the full definition of this science consisted of genus and differences. 5. Later certain authorities, expressing their position more fully, in their teaching divided perfect substantial definition into five divisions, as if into five organic parts. And the first of these deals with genus, the second with species, the third with difference, the fourth with proper quality, the fifth with accident. Chapter 26. On the categories of Aristotle. 1. Next follow the categories of Aristotle, which in Latin are called _praedicamenta_, within which all discourse is embraced throughout its various meanings. 5. There are ten sorts of categories, namely, _substantia_, _quantitas_, _qualitas_, _relatio_, _situs_, _locus_, _tempus_, _habitus_, _agere_, _pati_. 15. This work of Aristotle ought to be read with attention, since, as has been observed, whatever man speaks is included within the ten categories. It will help also to the understanding of the books that are devoted either to rhetoric or to logic.[233] [233] This passage is copied from Cassiodorus and is not an indication that Isidore had read the work of Aristotle that is mentioned. Chapter 27. On Interpretation (_de Perihermeniis_). 1. There follows next the book On Interpretation, which is extremely subtle and guarded in its various formulas and repetitions, of which it is said: “Aristotle when he wrote the Perihermeniae dipped his pen in intellect.” Chapter 28. On syllogisms. 1. Next follow the syllogisms of dialectic, wherein the advantage and excellence of that whole art is exhibited, the inferences of which greatly aid the reader in searching out the truth, so that the common error of deceiving an adversary by the sophisms of false conclusions disappears. 2. There are three formulae of categorical syllogisms. To the first formula belong nine modes....