[2.2.5] Stoic Ontology, Genus, Categories

“An examination of Stoic ontology might profitably begin with a passage from Plato’s Sophist. There, Plato asks for a mark or indication of what is real or what has being. One answer which is mooted is that the capacity to act or be acted upon is the distinctive mark of real existence or ‘that which is.’ The Stoics accept this criterion and add the rider that only bodies can act or be acted upon. Thus, only bodies exist. So there is a sense in which the Stoics are materialists or – perhaps more accurately, given their understanding of matter as the passive principle (see below) – ‘corporealists’. However, they also hold that there are other ways of appearing in the complete inventory of the world than by virtue of existing. Incorporeal things like time, place or sayables (lekta, see below) are ‘subsistent’ – as are imaginary things like centaurs.”

In this diagram I used OntoUML notation to present the main concepts of Stoic ontology:

Stoic categories based on Long, A. A. & Sedley, D. N. (1987). The Hellenistic Philosophers, Vol. 1 (p. 163). Cambridge: Cambridge University Press.
Comment texts from Stoic Ontology from Peter Wyss.
Something“This is the highest ontological genus: to be something (τί, ti) is to be some particular thing. Notably, this excludes Platonic Forms, or universals: they are not-somethings (outina), and thus ontological outcasts.” can be: Incorporeal; Body; Neither
Incorporeal“These do not exist, but subsist (ὑφεστάναι, hyphestanai); yet they are real (ὑπάρχειν, hyparchein). We can think of them as conditions ‘without which the interaction of bodies in the world would neither be analysable nor intelligible” can be: Sayable; Void; Place; Time
Body“Only bodies (σώματα, sômata) have being, or exist. Slogan: to exist is to have causal powers. Plato in the Sophist (247d–e): ‘Now, I say that what has some power to make something else into something, or to suffer the slightest, even once, this has real being. For I define being as nothing but power (δύναμις).’ The Stoic conception of existence is thus dynamic. Matter as such is passive, but bodies are not, since they are also infused by logos, which is active… only bodies can act or be acted upon ”
Neither can be: fictional entities (e.g. unicorns); limits can be: fictional entities; limits
Object_Substrate“A dog as merely an object, something ‘out there’, a discrete portion of matter: a substance (οὐσία, ousia). As object, a dog is merely the potential bearer of qualities” part of a Body
DisposedA dog as a further differentiated qualified thing: as running, barking, brave. associated with Body, one to zero or many multiplicity
Qualified“A dog as an object with certain qualities: bad breath, soft fur, dotted; can be qualified commonly as ‘dog’ or ‘furry’, or peculiarly as ‘Fido’.”associated with Body, one to zero or many multiplicity
RelativelyDisposed“A dog as an object in relation to other objects as owned by Jack, Rexs’ father winner at Crufts”associated with Body, one to zero or many multiplicity
OtherBodythe reference body of relatively disposed, e.g. Jack; father associated with RelativelyDisposed


  • All citations from: Baltzly, Dirk, “Stoicism“, The Stanford Encyclopedia of Philosophy (Spring 2019 Edition), Edward N. Zalta (ed.)
  • Peter Wyss, “Stoic Ontology
  • Long, A. A. & Sedley, D. N. (1987). “The Hellenistic Philosophers”, Vol. 1 (p. 163). Cambridge: Cambridge University Press.

First published: 06/03/2019

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