One of the most important (and difficult!) obstacles for students in classical Logic is understanding an illustration known as the “Porphyrian Tree” or the “Tree of Porphyry“.
This illustration explains how Aristotle’s “Categories” are divided from the “genus most general” down through all subalternate genera and species, down to the “species most special” and individuals. It is the key to understanding Aristotle’s art of Reasoning, but it takes some work to understand rightly.
Let’s take a careful look at the Porphyrian Tree above, and I’ll explain its meaning.
Explanation of the Porphyrian Tree
- Starting at the top of the tree, we see the word ENS, which means “BEING”.
- BEING is divided by two differences: PER SE and IN ALIO. This means “Being which is exists in itself.” and “Begin which exists in something else.” These are said to be the “Differences” that divide ENS into its two Species. You can read “DIVISIVA” in the branches connecting ENS to its differences. You can see two examples of these on the tree: SUSBTANTIA (Substance) and ACCIDENS (Accident).
- We then see the Difference PER SE connected to ENS, which constitutes the species SUBSTANTIA, and defines it: “A substance is a being that subsists in itself.”
- You can also see that the other Difference “IN ALIO” is repugnant or contrary to SUBSTANTIA.
- Like its Genus ENS, SUBSTANTIA is divided by two differences: CORPOREA (corporeal) and INCORPOREA (incorporeal). Examples are CAELUM (heaven) and SPIRITUS (spirit).
- The Difference CORPOREA connected to SUSBTANTIA constitutes the Species CORPUS (body), and is its definition: “A body is a corporeal substance.”
- We also see that SUBSTANTIA CORPOREA is repugnant to, or the opposite of SUBSTANTIA INCORPOREA.
- Next, SUSBTANTIA CORPOREA is divided by two Differences: ANIMATUM (living) and INANIMATUM (non-living). Examples are PLANTA (plant) and LAPIS (stone).
- The Difference ANIMATUM connected to SUBSTANTIA CORPOREA SUBSTANTIA constitutes the Species VIVENS (living body).
- We see that the species VIVENS is repugnant to the difference INANIMATUM.
- Next, VIVENS is divided by two Differences: SENSIBILE (sensible) and INSENSIBILE (insensible). Examples are ANIMAL (animal) and PLANTA (plant).
- The Difference SENSIBILE connected to VIVENS constitutes the Species ANIMAL (animal) and is its definition: “An animal is a sensible living body.”
- We see that the species ANIMAL is repugnant to the difference INSENSIBILE.
- Next, ANIMAL is divided by two Differences: RATIONALE (rational) and IRRATIONALE (irrational). Examples are HOMO (man) and an illegible name, possibly BESTIA (beast).
- The Difference RATIONALE connected to ANIMAL constitutes the Species HOMO (man) and is its definition: “A man is a rational animal.”
- We see that the species HOMO is repugnant to the difference IRRATIONALE.
- HOMO is the last of the Species on the tree and contains only INDIVIDUA (individuals). At the roots of the tree, we see the names of individual men.
This, then, is the meaning of the illustration known as the “Porphyrian Tree” or the “Tree of Porphyry”.
Different Branches of the Tree
Note that in this explanation, we only followed through one option at each division. For example, We divided ENS into SUBSTANTIA and ACCIDENS, but then chose SUBSTANTIA. We could have chosen ACCIDENS and investigated an entire different division of ENS. Likewise, after we chose SUBSTANTIA, we chose the difference COPOREA and ignored INCOPOREA. We did this throughout the rest of tree, choosing one of the two differences at each point and running to its end.
This tree can be used to explore all of Aristotle’s Categories, dividing all of the species of ENS into their subalternating Genera and Species until the Individuals they contain are reached.
This is the work of classical Philosophy.
If you would like to study this in more detail, please see chapter 3 of Porphyry’s Introduction to the Categories of Aristotle. We study this in Classical Reasoning I in the Classical Liberal Arts Academy.
God bless your studies,
William C. Michael, Headmaster
Classical Liberal Arts Academy
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