The five universals are described as the principles of tasawwur.

A meaning in the mind is called a concept, and when it exists outside the mind it is called an instance or referent. A concept is a universal when simply conceiving it does not stop many things from sharing in it, like the concept of the human being which applies to Ahmad, Zayd and Muhammad.

A concept is a particular when conceiving it does prevent sharing, such as the determinate Zayd with his individual features. There is a real particular and a relative particular, and that the relative particular is in truth also a universal. Universals can also be univocal, applying in the same way to all their instances, or gradational, applying with degrees.

The five universals are introduced as a special division of universals that will serve as the foundation for definition and for the rest of the logical course.

The origin of the term Isagoge and its link to the five universals

Some books say the five universals are a translation of the term Isagoge. This is corrected by showing that Isagoge in Greek simply means introduction. Porphyry the Syrian wrote an introduction called Isagoge to accompany the Organon of Aristotle.

The Organon consists of eight works, and Porphyry’s introduction was placed at the start of the book of Categories, which is the first of those works and is the place where Aristotle discusses the five universals.

When the Organon was translated into Arabic along with this introduction, some later writers thought that Isagoge itself meant the five universals.

In reality, Isagoge is only an introduction to the book in which the five universals are treated. This explains why the word became associated among Arabic writers with the chapter on the five universals, even though its real meaning is only introduction.

Division of the five universals into essential and accidental

The five universals are then divided into two main kinds.

• Essential
• Accidental

The word accident is something that stands opposite to essential, not as the technical opposite of substance in other discussions. The essential universal is what forms either the whole quiddity of a thing or a part of its quiddity. The accidental universal is what lies outside the quiddity. This is a different division from the earlier ones given for universals, and the text notes that divisions change according to the point of view taken.

From this perspective, the five universals are three essential universals, which either are the quiddity or enter into it as parts, and two accidental universals, which lie outside the quiddity but are still connected to it.

The species as the entire quiddity

The first essential universal is the species. The species is defined as the entire quiddity of a thing. In the example of the human being, the human is the species and is the whole human quiddity.

The concept of human being is universal because it can be predicated of many individuals in external reality, such as Zayd, Umar and Ahmad. The species is therefore an essential universal, since it is identical with the full reality of the thing and is predicated of many individuals.

The genus as a shared essential part

The second essential universal is the genus. It is defined as that part of the quiddity which is shared between this quiddity and other quiddities. In the case of the human being, when we define the human as a rational animal, the term animal is a part of the human quiddity and therefore essential. At the same time, it is shared with other species such as the horse and the donkey, which can be defined as a neighing animal or a braying animal.

Because this part of the quiddity is shared between the human and other species, it is called the genus. The text stresses that the genus is an essential universal, since it enters into the complete reality of the species while still being shared with other realities.

The differentia as a specific essential part

The third essential universal is the differentia. It is the part of the quiddity that is confined to that quiddity alone and does not occur in other species. In the definition of the human being as a rational animal, the term rational is the differentia.

It enters into the human quiddity as part of the complete definition, so it is essential, but it is not shared with other animals. One cannot say that the horse or the donkey is rational. Rationality distinguishes the human species from other species, which is why it is called the differentia.

Another example is a horse. The horse is the species and is defined as a neighing animal. Animal is again the genus, since it is shared between the horse and other animals, while neighing is the differentia, since it is confined to the quiddity of the horse alone. Neighing is described as an essential universal, because it is part of the complete definition of the horse, even though it is not the quiddity itself.

The specific accident as a proprium

The first accidental universal is the specific accident, which the text calls the proprium. It is an attribute that lies outside the quiddity, but once the quiddity exists this attribute is confined to it alone. It is external to the essence, yet uniquely accompanies that essence. The classical example given is laughing in relation to the human being.

Laughing is not included in the definition of the human being as a rational animal, so from the point of view of definition it is not part of the quiddity.

Once the human quiddity exists, laughter is singled out as something that belongs specifically to humans and does not belong to other animals in the same way. For this reason the logicians treat laughing as a proprium, a specific accident attached to one species.

There is a problem in the criteria that decide what is truly part of a quiddity and what is an accident outside it, because some of their distinctions are not firmly established and lead to confusion.

The common accident as a general external attribute

The second accidental universal is the common accident. It is also an attribute that lies outside the quiddity, but it is not confined to any one species or quiddity. Instead, it is a general attribute that can be predicated of different kinds of things. The example given is walking in relation to the human being. Walking is not part of the human essence and is not unique to humans, since many animals walk. It is therefore a universal that is accidental and general, not specific, and is called the common accident.

Summary of the division into five universals

We have five universals which serve as the principles of conceptual knowledge in logic. Three of them are essential universals. These are the species, which is the entire quiddity, the genus, which is the part of the quiddity shared with other species, and the differentia, which is the part of the quiddity confined to that species and distinguishing it from others.

Two of them are accidental universals. These are the proprium, which lies outside the quiddity but is confined to that species when it exists, and the common accident, which lies outside the quiddity and is not confined to it but is shared more widely.

The series of universals, proximate and remote genus

Universals can be arranged in a series from the most general down to the most specific. Using the human being as an example, the broadest universal is existent. Under that stands body, then living body, then animal, then human being.

The concept closest to the species is called the proximate genus, which in the case of the human being is animal. The broader concepts above it, such as living body and body and existent, are called remote genera in relation to that species. The more remote a genus is, the broader its concept and the more individuals it covers.

The species itself is predicated directly of individuals, such as Zayd or Ahmad, while the genus is predicated of several species, such as humans, horses and donkeys. From one angle the species is a universal in its own right, and from another angle it is a relative part when compared to a more general concept like animal.

The five universals as predicables and their role in definition

These five universals are often called the five simple notions, because they are simple terms, or the five predicables, because they typically appear as predicates in propositions such as “Zayd is a human” or “Zayd is an animal.” It is rare to treat the universal itself as the subject in ordinary speech. The author mentions that some older books even refer to them as the five categories, meaning the five predicables.

The five universals are directly tied to the subject of definition. In logic, what is defined is the species, which is an essential universal.

To define the species, one uses the remaining four universals, sometimes by joining the proximate genus to the differentia in a complete definition, and sometimes by using a proprium or a common accident in forms of description.