Category of being

In ontology, the different kinds or ways of being are called categories of being or simply categories. To investigate the categories of being is to determine the most fundamental and the broadest classes of entities. A distinction between such categories, in making the categories or applying them, is called an ontological distinction.

The categories of being, or simply "the categories", are defined as the highest classes under which all elements of being, whether material or conceptual, can be classified. These categories belong to the realm of philosophy and the difference between categories and classes was described by the philosopher C.I. Lewis as that of a hierarchical tree or pyramid where the most general categories such as those of logic are to be found at the top and the least general classes such as species of animal at the bottom. There are therefore two main areas of interest (i) at the top of the tree—how being first divides into discrete or overlapping subentities, and (ii) at the bottom of the tree—how the different elements can be correlated into higher classes. The structure may consist of a simple list such as the one produced by Aristotle or it may be composed of headings and subheadings such as the tables produced by Immanuel Kant. The elements of being are commonly seen as "things", whether objects or concepts, but most systems will also include as elements the relations between the objects and concepts. The distinction is also made between the elements themselves and the words used to denote such elements. The word "category" itself is derived from the Greek κατηγορία (katigoría), meaning to predicate, and therefore the categories may also be thought of as kinds of predicates that may be applied to any particular subject or element, and by extension to the concept of being itself.

If we take any subject and with it form a sentence "the subject is…" then in a valid system of categorisation all the different things we can say about the subject should be classifiable under one of the categories within the system. Aristotle listed ten categories amongst which we find, for example, the three categories of Substance, Quality and Quantity. In Heidegger’s example "This is a house. It is both red and tall" the word "house" can be classified under Substance, "red" under Quality and "tall" under Quantity. The subject, the house, gathers around it what was called in the 19th century a "colligation of concepts" or in the 20th century a "bundle of properties" all of which serve to define the house. By extension we can say that all being consists of nothing but Substance, Quality, Quantity and the rest, because nothing else can be said of the subject. Categorisation has raised many problems throughout the history of philosophy, including those of the number and types of category, how the categories interrelate with one another and whether they are real in some way or just mental constructs, and to introduce the many different solutions that have arisen it is worth considering the history of the categories in brief outline.

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