Introduction

Now that we have covered the predicables related to what is generally entitled ‘secondary substances’ (ie. that which is said of something, but is not in a substrate), it is time to elucidate that which is both said of something, as well as is in something.

Common Accident

The most rudimentary of these terms is the term ‘common accident’. A common accident is something which is in a substrate, which is not conducive to an account of a subject, and can be said to be in other substrates equally therein. One example may be ‘blue’. If, for instance, a pencil is blue, we may therein say it is blue in the same way the sky is blue, or water is blue. Moreover, if a blue pencil stopped being blue, there would be no effect to the account of the pencil. The pencil would remain a pencil, formally and essentially. Therefore, common accidents are removable. Another important idea to consider is that there is no convertability within accidents. If we know a given pencil is blue, there is no way to return to the pencil after we arrive at blueness. This is different from the manner in which if we know that if something is, for instance, riseable (that is, capable of laughter), it is a human, because only humans are capable of laughter.

Property

Now, with this prelude, we can examine that which is a property. A property is something which belongs to a substrate and is peculiar to that substrate. The previous example is sufficient, that is, riseability in humans. There is assured convertibility herein, whereby if one knows something has a property, the account of this thing assured. Furthermore, the property can be either accidental to the thing.

Differentia

That which is defined as a modifying article that separates a genus into species through some essential quality particular to the species. That is, a species is to be defined through a combination of terms, the first being the genus which predicates the species, and the second being the differentia, a property of a substance, essential in nature, which clarifies what sort of thing it is, and how it is different from other species of the genus. A common example of a differentia is “rational” when used in the manner of pronouncing “man is a rational animal”. Herein, we are predicting two things of man. The first is an essential quality (ie. ‘rational), the second being a broader secondary substance (‘ie. ‘animal’). Thus, we arrive at an account of a species through utilizing both a differentia and a genus.

One may posit herein that this terminology seems arbitrary. One may say, “what makes the differentia something separate from other properties of a substrate? The answer is that the differentia is contained within the account of a thing, while the property is not. Hence, the differentia is essential while the property is not necessarily. Furthermore, a differentia can be present in multiple thing, and is only relevant in terms of giving account to separate species from genera. One example is that of bipedalism, which is a differentia rather than a property, because if one wishes to differentiate humans from other primates, one could say “man is a bipedal primate”, however, one could also use the term “bipedal” in order to describe birds. Therefore, it is notable that while a property exists in only one species, differentia can exist in many, and, moreover, that the differentia is only differentia when paired with a genus.