CLAA – TRV-371 - Porphyry, Introduction, Chapter 6

Classical Liberal Arts Academy
Mr. William C. Michael, O.P.
05/07/2026

Lesson Text: Porphyry, Introduction. Chapter 6

Introduction

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“Lord our God, in your wisdom and love you surround us with the mysteries of the universe. Send your Spirit upon us and fill us with your wisdom and blessings. Grant that we may devote ourselves to our studies and draw ever closer to you, the source of all knowledge. We ask this through Christ our Lord. Amen.”

Prelection

In this lesson, we will study Porphyry’s Introduction, Chapter 6

Porphyry was born about AD 234 in Tyre, a city of Phoenicia. He was educated in rhetoric and philosophy, and later came to Rome where he became a disciple of Plotinus, under whom he advanced deeply in the study of philosophy. He devoted his life to study, teaching, and writing, and is especially known for editing and arranging the works of his master, as well as composing many treatises of his own, including the Isagoge. He died about AD 305, after a life given to philosophical inquiry, and is chiefly remembered as a principal transmitter of Neoplatonism and as the author of a work that served as a foundation for logical studies throughout the medieval schools.

Porphyry’s Introduction (Isagoge) was written as a preparation for the study of Aristotle’s Categories and serves as one of the clearest introductions to the basic ideas of logical thought. In it, Porphyry explains the five predicables—Genus, Species, Difference, Property, and Accident—which help students understand how we define and classify things. Throughout the Middle Ages, this work was studied by Catholic students as the first step in the study of logic and philosophy. Its importance for classical Catholic students lies in the fact that it trains the mind to think clearly, distinguish carefully between different kinds of ideas, and reason according to reality rather than confusion or opinion. By studying Porphyry, students begin to develop the intellectual habits needed for later studies in Aristotelian philosophy, Scholastic theology, and the liberal arts.

The objective of Chapter 6 of Porphyry’s Introduction is to compare and contrast the five predicables—Genus, Species, Difference, Property, and Accident—after defining them individually in the previous chapters. Porphyry explains what they all have in common, namely that they are predicated of many things, and then carefully distinguishes the different ways each is predicated of species and individuals. By adding concrete examples, he helps students move from simple definitions to a clearer and more practical understanding of logical classification and predication.

The historical significance of this chapter lies in its role in the traditional study of logic throughout the Middle Ages. Christian students in cathedral schools and universities studied these distinctions as part of their preparation for Aristotle’s logical works and later Scholastic theology. The careful comparison of the predicables trained students to think precisely about definition, classification, and the essential versus accidental qualities of things—skills that became foundational for classical philosophy, theology, law, and scientific reasoning.

Division of Text

Introduction
Having separately discussed…
How Predicables are Similar (Comparison)
It is common therefore…
How Predicables are Different (Contrast)
But Genus is predicated of the Species…
Examples of Predicables
For animal is predicated of horse

Exposition

Part 1: Introduction

1. Having separately discussed all that was proposed, I mean, Species, Difference, Peculiarity, and Accident, we must show what things are common to them, and what are peculiar.

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Part 2: How Predicables are Similar (Comparison)

2. It is common therefore to all of them to be predicated, as we have said, of many things.

Part 3: How Predicables are Different (Contrast)

3. But Genus is predicated of the Species and individuals which are under it; and in a similar manner Difference.

4. Species is predicated of the individuals which are under it; but Peculiarity is predicated of the Species of which it is the Peculiarity, and of the individuals which are under that Species.

5. And Accident is predicated both of Species and individuals.

Part 4: Examples of Predicables

6. For animal is predicated of horse and ox which are Species (of it); and also of this particular horse, and that particular ox, which are individuals.

7. But the irrational is predicated of horse and ox, and of particular horses and oxen.

8. Species however, such as man, is alone predicated of particulars.

9. But Peculiarity, is predicated of the Species of which it is the Peculiarity, and of the individuals under that Species.

10. Thus, risibility is predicated of man, and of individual men.

11. But blackness is predicated of the Species of crows, and of individual crows, since it is an inseparable Accident.

12. To be moved likewise, which is a separable Accident, is predicated of man and horse.

13. Primarily, however, it is predicated of individuals; but secondarily, of those things which comprehend individuals.

Memory

The following sentences summarize the key points of this lesson and are recommended for memorization.

All predicables are said of many things.
Genus is said of species and individuals under it.
Difference is said of species and individuals under it.
Species is said of the individuals under it.
Peculiarity is said of its species and the individuals under it.
Accident is said of species and individuals.
Inseparable accident is always present (e.g. blackness in crows).
Separable accident may or may not be present (e.g. being moved).
Accidents are said primarily of individuals, secondarily of species.

Conclusion

In this class, we have studied Chapter 6 of Porphyry’s Introduction to the Categories. We have discussed how the five predicables—Genus, Difference, Species, Peculiarity, and Accident—each work differently when we use them to say something about things. We have learned that Genus and Difference are predicated of both Species and individuals, that Species is predicated only of individuals, that Peculiarity is predicated of both Species and individuals, and that Accident is predicated of both Species and individuals. We have also learned that predication is primarily about individual things, but secondarily about the universal concepts that gather many individuals together.

Support

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