Understanding Chapter 11 of Porphyry’s Introduction

Students often have a difficult time understanding chapter 11 in Porphyry’s Introduction, but this is actually very simple.

In the Introduction, Porphyry is explaining the five kinds of things that can be predicated of subjects, known as the five predicables: Genus, Difference, Species, Peculiarity and Accident.

In chapter 11, Porphyry writes:
“It would seem that all the differences produced are twenty”.

What in the world is he talking about?

Porphyry is comparing and contrasting the five predicables. So, each of the five will need to be compared with the four others. Therefore, we should expect 20 comparisons–4 comparisons for each of the 5 predicables.

Porphyry explains that this, however, is not necessary because when we compare Genus with Difference, we do not then need to compare Difference with Genus, again. So, for each predicable, we will only need to compare it with the predicables to which it has not already been compared.

1. Genus vs. Difference, Species, Peculiarity, Accident (4)
2. Difference vs. Species, Peculiarity, Accident (3)
3. Species vs. Peculiarity, Accident (2)
4. Peculiarity vs. Accident (1).

This makes for a total of 10 comparisons necessary–not 20.

That’s all that Porphyry is saying in lesson 11.  Simple.

God bless your studies,

Mr. William C. Michael