E.J. Lowe’s four-category ontology (2006) is an attempt to answer the question of what are the fundamental categories of being, as well as the question of what are the basic distinctions between them. Lowe explains that ontological categories are kinds of being.1 The distinctions between ontological categories include the distinction between universals and particulars, and the distinction between substances and non-substances. Thus, there are four basic ontological categories: substantial universals (kinds), substantial particulars (objects), non-substantial universals (attributes), and non-substantial particulars (modes).
Substantial universals are instantiated by substantial particulars, and non-substantial universals are instantiated by non-substantial particulars. Kinds are instantiated by objects, and attributes are instantiated by modes (or “tropes”). For example, a particular tomato is an instance of the kind, “tomato,” and a particular redness (e.g. the redness of a particular tomato) is an instance of the attribute, “redness.”2
Lowe explains that objects (individual substances) are particular instances of kinds (substantial universals). Modes (property or relation instances) are particular instances of attributes (property or relational universals).
The relations between the four basic ontological categories can be schematized as an “ontological square,” in which the category of “kinds” is in the upper left corner, the category of “objects” is in the lower left corner, the category of “attributes” is in the upper right corner, and the category of “modes” is in the lower right corner. Kinds are characterized by attributes, and are instantiated by objects. Attributes are exemplified by objects, and are instantiated by modes. Objects are characterized by modes (ways of being, or particular instances of properties and relations). Thus, there are three basic kinds of relations between members of the four basic ontological categories: instantiation, characterization, and exemplification.3
Lowe admits that there are at least two basic assumptions made by the four-category ontology: that universals exist, and that there is a basic distinction to be made between substantial and non-substantial universals.4
A problem that must be addressed by the four-category ontology is that of whether there can be second- or higher-order kinds of being, as distinguished from first-order kinds of objects. Lowe recognizes this problem, and he explains that according to his definition of “kinds” as universals that are instantiated by substantial particulars, kinds are instantiated by objects and not by other kinds (substantial universals). An ontological category, such as “kinds,” is a kind of being, but it is not a kind in the sense that a kind of object is a kind. However, the counter-argument can also be made that “kinds” as an ontological category can be instantiated not only by kinds of objects, but also by kinds of modes, properties, and relations.
Another problem is that of whether kinds, attributes, and modes may also be made objects (of perception, thought, observation, and investigation). If kinds, attributes, and modes themselves may be made objects, then objects may not be able to be defined exclusively as instances of kinds.
Another problem is that of whether there may be second- or higher-order properties and relations (properties of properties, and relations of, or between, relations). According to Lowe’s definition of attributes as universals that are instantiated by non-substantial particulars, attributes are instantiated by modes (property or relation instances), and not by other attributes (property or relational universals).
Another problem is that of whether the instantiation of kinds or attributes is any different from their exemplification. Particular instances of kinds or attributes may be individual examples of those kinds or attributes. For example, if a particular tomato instantiates the kind, “tomato,” then it also exemplifies it. If a particular redness (e.g. the redness of a particular tomato) instantiates the attribute, “redness,” then it also exemplifies it. On the other hand, a particular tomato may exemplify the property of “redness” without actually instantiating it (because the property of “redness” may be instantiated by the redness of that particular tomato, rather than by the tomato itself). What then is the nature of the difference between instantiation and exemplification?
Lowe recognizes all these problems, and he attempts, with varying degrees of success, to resolve them. His four-category ontology is a very thought-provoking attempt to define the nature and kinds of being, and it is a brilliantly conceived and clearly formulated effort to advance our understanding of the categorical construction of reality.
1E.J. Lowe, The Four-Category Ontology: A Metaphysical Foundation for Natural Science (Oxford: Clarendon Press, 2006), p. 20.
2Ibid., p. 22.
3Ibid., p. 23.
4Ibid., p. 28.