Ontology is the branch of metaphysics which deals with the study of being, existence and reality. It concerns the categories of being of both the physical (objects) and the abstract (categories, properties, etc.) and attempts to create clear conceptions of the metaphysical relationships.
Categories of Being
The categories of being are categories which are extended to objects of inquiry. These categories usually include: physical object, mind, classes, properties, relations, space and time, propositions, and events. The relations between these categories are disputed by metaphysicians.
Descartes considered extension the primary property of physical objects. According to this definition, a physical object, then, must necessarily exist in two dimensions, and must have mass. Historically, it has been maintained (notably by Spinoza) that subjects belonging to one category of being can only act on other subjects in the same category. So, physical objects can only act, and be acted on by, other physical objects.
Ontological status pertains to the existence of a subject under particular circumstances, and is distinguished by John Searle as being a matter of subjectivity and objectivity. An object has a subjective ontology if it exists only in the presence of a mind representing the subject. An object has an objective ontology if its existence is not dependent on the presence of a mind representing the subject. For Searle, subjective ontology is, first and foremost, a property of minds themselves (as the major property of a mind is its ability to represent itself).
- Example: A rock falls into a pond. The event has objective ontology.
- Example: Al and Bob make an agreement that they will not steal from each other. The agreement has a subjective ontology.
The matter of distinction is over whether or not the subject (the rock or the reflection) would 'exist' in the event that the mind was absent. In the case of the rock, the explanation is simple enough. The rock falls into the pond regardless of whether or not there is a mind there to represent it. In the case of the agreement, the agreement only exists as long as the minds of Al and Bob are representing the agreement. Searle refers to the agreement as a social fact, in contrast to the rock falling into the pond, which is a fact per the Tractatus.