„Being [ὂν] is spoken of in many ways [...]. For one type of being signifies the what-it-is [τί ἐστι] and a this [τόδε τί]; another signifies quality, or quantity, or any of the other things predicated in this way. But while being is spoken of in this many ways, it is evident that among these the primary being is the what-it-is, which signifies substance.” (Aristotle: Met. VII, 1, 1028a10-14)

As shown in the quote above, “being” is in many different ways in Aristotle’s way of thinking: as a primary substance in one single thing, and as an accident as something not essential to the single thing in the form of predicates. Metaphysics is „first philosophy” for Aristotle as it is the study of being qua being and thus, the analysis of the first principles and causes (Met. I, 1, 982a1-3).

Aristotle begins his logical thinking with the predicative sense of a sentence such as „the grass is green”. The copula „is” however doesn’t elucidate “being”. “Is” as the logical prediction is the starting point from which he develops the ten distinct categories by combining theory of language and ontology. This way he divides substance into the definition of a primary (πρώτη οὐσία) and a secondary substance and develops his scheme of accidents by means of different categories. The primary substance as the first and fundamental category denotes the single thing, be it an individual person, plant or animal that is not predicated of a subject. It is his form and essence. The secondary substance is the ultimate substratum [ὐποκείμενον] (Met. V, 7, 1017a5-20 und V, 8, 1018a24) such as the species and genera of primary substances („Socrates is human”). The other nine categories apply to accidents that only exist in subjects and are therefore variable, interchangeable and are predicated of a subject such as quality, relation etc.

Substance (object or thing) and accident (properties) are thus different metaphysical entities, that is to say they are primary and secondary, categorical classifications of being. The difference is understood in modal terms: “being in itself” vs. “being only in another thing”, in contrast to Plato’s distinction of being transient or material.


  1. This is Socrates. (Substance / οὐσία)


  1. Socrates is a philosopher. (Quality)
  2. Socrates is Xanthippe’s husband. (Relation)              (Accident / συμβεβηκός)
  3. Socrates is in Athens. (Place)