Four categories

Jonathan Lowe has proposed that the four fundamental categories of things in the world are: substances, kinds, modes, and properties (Lowe 2006). Substances and modes are individual or particular; kinds and properties are universal. Substances are independent; modes are dependent on substances. Their respective species, namely kinds and properties, are themselves generically dependent on instances, but properties are also indirectly dependent on kinds in that there could not be properties unless there were instances thereof, i.e. modes, there could not be modes unless there were substances, and there cannot be substances that are not of a kind, so properties are indirectly dependent on kinds.

This four-category ontology has a venerable pedigree, going back to Aristotle. In Book 2 of the Categories, Aristotle divides things ‘said without combination’ into those which are and those which are not said of a subject, and those which are and those which are not in a subject, where by ‘in’ Aristotle explains he means ‘in not as a part, but as unable to exist without’ what they are in, i.e. dependent. So the four categories arise from the crossing of two distinctions: the said of/not said of distinction, and the in/not in distinction. Aristotle calls those things which are not in something substance, whether first (individual) or second (universal, or kinds). Those things which are in something are accidents (symbebeka).