former); e. g. if a man should say, that it is contingent, for "a man," not to be "a horse," or for "whiteness" to be present with no "garment." For of these, the one, is necessarily not present, but the other, is not necessarily, present; and the proposition is similarly convertible, for if it be contingent to no "man" to be "a horse," it also concurs with no "horse" to be "a man," and if "whiteness" happens to no "garment," a "garment" also happens to no "whiteness;" for if it did happen to any, "whiteness" will also necessarily happen to "a certain garment," and this has been shown before, and in like manner with respect to the particular negative proposition. But whatever things are called contingent as being for the most part and from their nature, (after which manner we define the contingent,) will not subsist similarly in negative conversions, for an universal negative proposition is not converted, but a particular one is, this however will be evident when we speak of the contingent. At present, in addition to what we have said, let thus much be manifest, that to happen to nothing, or not to be present with any thing, has an affirmative figure, for "it is contingent," is similarly arranged with "it is," and "it is" always and entirely produces affirmation in whatever it is attributed to, e. g. "it is not good," or, "it is not white," or in short, "it is not this thing." This will however be shown in what follows, but as regards conversions, these will coincide with the rest.
Chapter 4
These things being determined, let us now describe by what, when, and how, every syllogism is produced, and let us afterwards speak of demonstration, for we must speak of syllogism prior to demonstration, because syllogism is more universal, since, indeed, demonstration is a certain syllogism, but not every syllogism is demonstration.
When, then, three terms so subsist, with reference to each other, as that the last is in the whole of the middle, and the middle either is, or is not, in the whole of the first, then it is necessary that there should be a perfect syllogism of the extremes.
