Porphyry’s Isagoge

1Porphyry of Tyre

Porphyry was born in Tyre in Phoenicia (today in Lebanon) in the third century CE. His exact dates are uncertain: the Stanford Encyclopedia of Philosophy gives 234?–305?, the Syriac heritage dictionary ca. 232–ca. 305, and the Turkish encyclopaedia of Islam (TDV) gives his death as 304. His native name was Malkos, ‘king’, which became Basileus (‘king’) in Greek.

He studied in Athens with the Platonist Longinus and then, from 263 to 269, in Rome with Plotinus, the founder of what is now called Neoplatonism. In 268, on Plotinus’ advice, he went to Sicily to recover from a depression and stayed there beyond his teacher’s death in 270. Around 301 he edited Plotinus’ writings as the Enneads, with a Life of Plotinus as preface.

Some sixty works are attributed to him, most of them now lost or fragmentary, including his polemic Against the Christians. Unlike Plotinus, Porphyry was inclined to reconcile Aristotle with Plato. He was the first Platonist to write proper commentaries on Aristotle’s logical works, and he made the Categories a basic text in the Neoplatonic schools. In Arabic he is called Furfūriyūs (فُرْفُورِيُوس).

2When and why he wrote it

The book opens with an address to a pupil, Chrysaorius: to understand Aristotle’s Categories, and also for giving definitions, it is necessary to know what genus, difference, species, property and accident are. Porphyry promises to set out briefly, in the manner of an introduction, what the older philosophers taught about these five, leaving the deeper questions aside.

According to the ancient commentators Ammonius, Elias and David, the work was sent to Chrysaorius; modern reference works place its composition in Sicily during Porphyry’s stay there, about 268–270. The Stanford Encyclopedia does not date the work, so this date rests on the later commentators’ report.

The Isagoge is short and its aim is practical. It does not discuss the ten categories themselves but gives the reader the vocabulary with which Aristotle and his commentators talk about how one term is said of another.

3The five terms

Porphyry explains five ways in which something can be said (predicated) of something else. A genus, such as ‘animal’, is said of several things that differ in species. A species, such as ‘human’, is what falls under a genus. A differentia, such as ‘rational’, is what distinguishes a species within its genus. A property (proprium) belongs to one species only, like being able to laugh for humans. An accident is what can come and go without destroying its subject.

Aristotle himself, in the Topics, had sometimes treated four kinds of predicate (definition, property, genus and accident) as covering all predication. Later commentators replaced definition with species and differentia and so arrived at the five ‘predicables’, in Latin the quinque voces, ‘five words’. In Arabic they became the five universals, al-kulliyyāt al-khams: jins, nawʿ, faṣl, khāṣṣa and ʿaraḍ ʿāmm. Al-Abharī’s Īsāghūjī illustrates the proprium with the classic example ‘laughing’ (ḍāḥik) for the human being.

After defining the five, the second half of the book compares them two by two: what genus and difference have in common and how they differ, then genus and species, genus and property, and so on through every pair. Later readers, including Ibn Sīnā, judged this second part less useful than the first, but it shows Porphyry’s method of marking out each term against the others.

4The ‘Porphyrian tree’

In the chapter on genus and species Porphyry illustrates how terms are ordered from the most general to the most particular. Substance is the highest genus; under it is body; under body, animated body; under that, animal; under animal, rational animal; under that, human; and under human, individuals such as Socrates and Plato.

Each term in the middle of this chain is a species of the one above it and a genus of the one below. Substance is a genus only, the most general; ‘human’ is a species only, the most specific. Individuals such as Socrates are not species at all, because they cannot be divided further.

Medieval textbooks drew this chain as a tree, the ‘Porphyrian tree’, and used it to illustrate Porphyry’s classification of substance. The ideas behind it (a highest genus, intermediate terms that are both genus and species, and a lowest species above the individuals) return in the Arabic commentaries on the five universals.

5The questions he set aside

At the start of the book Porphyry deliberately leaves three questions about genera and species unanswered: whether they really exist or are only in our thoughts; if they exist, whether they are bodies or incorporeal; and whether they exist separately or in sensible things. Such questions, he says, are very deep and need a longer inquiry than an introduction allows.

These few lines had a long afterlife. Through Boethius’ Latin commentaries they became the starting point of the medieval debate on the ‘problem of universals’. In the Arabic tradition, Ibn Sīnā took up the status of universals in his reworking of the Isagoge, where, as his modern editor puts it, the doctrine of predicables stands ‘at the crossroads between logic and metaphysics’.

For a beginner the lesson is the same one Porphyry intended: one can learn to use genus, species and the rest correctly in logic before deciding what universals ultimately are.

6Why it mattered

In the school of Ammonius at Alexandria (late fifth and early sixth century), the course in philosophy began with an introduction to philosophy, then Porphyry’s Isagoge with a commentary, then an introduction to Aristotle, and then the Categories. Porphyry’s small book thus became the door to the whole of Aristotle, and it kept this place in Byzantium, in the Syriac and Arabic worlds, and in the Latin West.

In Arabic it was the only work of Porphyry whose translation survives. It was counted with Aristotle’s logical works as the first part of the Arabic Organon. Later Arabic handbooks, al-Abharī’s among them, likewise begin with utterances and the five universals before turning to definition, propositions and syllogism, and al-Abharī’s still carries Porphyry’s title.

The Greek text was edited by Adolf Busse (Commentaria in Aristotelem Graeca IV.1, Berlin, 1887). Jonathan Barnes published an English translation with a full commentary (Oxford, 2003), and older English translations are freely available online. TDV notes Turkish translations by Hamdi Ragıp Atademir and by Betül Çotuksöken.