We shall now embark on the nature of the five Aristotelian predicables. First, we should define what a predicable is. A predicable can simply be defined as a system of relations that describe how a thing is of many. The first form of predicable is the genus. The ancient meaning of the word genus can be defined in multiple senses. A genus could mean a set of things related to one another because all are related to some one thing in a particular manner. In this way, we could say that the descendants of Abraham are a genus because of their collective kinship to Abraham. Genus could also imply wherein someone is born, ie. Aristotle of Stagira. A third sense is that grouping wherein there are subordinate groupings (species). This third definition is what we shall employ in our philosophy. Therefore, the definition by which we shall grant genus is “that predicated essentially of many things which differ in species”. Genera, (plural of genus), therefore, differ from those terms which are predicated of an individual thing, because they’re explained as being predicated of many things. However, they differ from species in that although species is predicated of many things, the many do not differ in species except in number. For instance, man as a species is predicated of Aristotle and Plato, who do not differ in species, but in number. But animal, a genus, is predicated of man, ox and horse, which differ in species as well as number.

Genus is also different from difference and accidents, for, although accidents and differentia are predicated of many things differing in species, they are not predicated essentially. Therefore, we conclude genus is predicated of many things, differs from individual terms which are predicated of only one thing, since the genus is a genus of things that differ in species, it differs from terms predicated as species or properties, and, finally, since it’s predicated essentially, it’s separate from differences and accidents, of which is predicated qualitatively.
Moving on, although the Greek term for the noun ‘species’, which was eidos, in colloquial usage generally referred to the “shapeliness” of an individual, we shall define it as that which is under a defined genus. Hence, for the genera [plural of genus] color, animal, and figure, we offer three species under these three genera, which are, respectively, white, elephant, and square. Previously, we had defined genus as that which consists of species, and now, we are defining species as that which belongs to a particular genus. Therefore, we better develop a superior definition for the terms.

Porphyry, in his Isagoge, related the followers of Aristotle defined species as “what is ordered under a genus and what the genus is predicated of essentially”. They also stated that species is “predicated essentially of many things which differ in number”. However, this secondary definition will only define the lowest species (ie. that which is a species only), and the former definition shall suffice for any higher species. To explain, realize that in each category there shall be higher classes, lower classes and some within the medium of these extremes. There is a certain highest genus, and a certain lowest species. And between these two, there remain an assortment of genera and species, in which some are both, due to their relations to the highest genus and lowest species. Allow us to make this meaning clear by using one of Aristotle’s ten categories which we shall expand upon further. Substance is, in and of itself, a genus. Under substance is body, and under this is animated body, under which is animal, under which is rational animal and under which is man, under man are particular men like Plato, Socrates and Aristotle. Of these, substance is the highest genus, and the lowest species is man. Animal is a genus of rational man, whilst being a species of animated bodies. However, while man is a species of rational animals, it is NOT a genus of particular men, rather, it is the lowest species. Therefore, every species which is predicated immediately prior to individuals shall never be a genus. Likewise, substance is the highest genus, as it is none higher than it. The intermediate classes shall be species of prior classes and genera of posterior classes.

Following this, we shall realize that intermediate classes have two relationships. The first of these relationships are with prior classes of which they are species and posterior classes of which they are genera. The extremities, however, have one single relation. The lowest species can be called both a species of individuals as that which is below it is not a species of anything, and, a species of prior classes, as it is contained by them

Moreover, we shall lay down ten genera as primary sources which we shall review later. Thus, if anyone names all things beings, he shall do so homonymously, but not synonymously, for if being were a common genus of all, all things would be called beings synonymously. Thus, there is community amongst the ten primary genera in name only, none according to the definition of the word. Moreover, there are ten highest genera, whilst there is an indefinite, though finite, number of lowest species. Individuals, according to Aristotle, are infinite. This is the reason Plato, in his Sophist, Statesmen and Philebus, urges us to stop at the lowest species after originating from the highest genera. He states there is no such thing as knowledge of individual things, rather, only of the lowest species which we arrive at by differentiating the intermediary species. It is notable that there is no convertibility amongst the species and genera, due to the reason that equals must be predicated of equals, such as the neighing of the horse, or of the greater of the lesser, such as animal of man, but never the lesser of the greater, such as elephant of animal. You can say man is animal, but cannot say animal is man.