Generally, either the study of being, or a particular theory of what there is (as in ‘Smith’s ontology contains classes but not propositions’, meaning that Smith believes there are such things as classes but not such things as propositions).
More specifically, part of the logical system underpinning the mereology of Polish logician Stanislaw Lesniewski (1886-1939). The system uses three types of names -proper names (‘Socrates’), common names (‘dog’), and fictitious names (‘Apollo’, ‘centaur’) – and elaborates the relations between a complex set of connectives that can be applied to them; for example, ‘is a’ (‘Socrates is a man’), ‘overlaps’ (‘Some cats are pets’), and so on.
The other part of Lesniewski’s logical system is called protothetic, a sort of generalization of the standard logic of propositions.
C Lejewski, ‘On Lesniewski’s Ontology’, Ratio (1958)
The compound word ontology (‘study of being’) combines
- onto- (Greek: ὄν, on; [note 1] gen. ὄντος, ontos, ‘being’ or ‘that which is’) and
- -logia (-λογία, ‘logical discourse’).
While the etymology is Greek, the oldest extant records of the word itself, the New Latin form ontologia appeared
- in 1606 in the Ogdoas Scholastica by Jacob Lorhard (Lorhardus), and
- in 1613 in the Lexicon philosophicum by Rudolf Göckel (Goclenius).
The first occurrence in English of ontology, as recorded by the Oxford English Dictionary, came in 1664 through Archelogia philosophica nova… by Gideon Harvey The word was first used, in its Latin form, by philosophers, and based on the Latin roots (and in turn on the Greek ones).
Gottfried Wilhelm Leibniz is the only one of the great philosophers of that century to have used the term ontology.
Ontology is closely associated with Aristotle’s question of ‘being qua being’: the question of what all entities in the widest sense have in common. The Eleatic principle is one answer to this question: it states that being is inextricably tied to causation, that “Power is the mark of Being”. This answer assigns fully real, concrete, or factual existence to actual singular particular processes, events, or natural objects, in the ordinary world, as distinct from abstractions, generalities, and fictions, which it regards as conceptually or perceptually contingent, imagined or derived from reality. A contrasting but little accepted answer can be found in Berkeley’s slogan that “to be is to be perceived”. Intimately related but not identical to the question of ‘being qua being’ is the problem of categories. Categories are usually seen as the highest kinds or genera. A system of categories provides a classification of entities that is exclusive and exhaustive: every entity belongs to exactly one category. Various such classifications have been proposed, they often include categories for substances, properties, relations, states of affairs or events. At the core of the differentiation between categories are various fundamental ontological concepts and distinctions, for example, the concepts of particularity and universality, of abstractness and concreteness, of ontological dependence, of identity and of modality. These concepts are sometimes treated as categories themselves, are used to explain the difference between categories or play other central roles for characterizing different ontological theories. Within ontology, there is a lack of general consensus concerning how the different categories are to be defined. Different ontologists often disagree on whether a certain category has any members at all or whether a given category is fundamental.
Particulars and universals
Particulars or individuals are usually contrasted with universals. Universals concern features that can be exemplified by various different particulars. For example, a tomato and a strawberry are two particulars that exemplify the universal redness. Universals can be present at various distinct locations in space at the same time while particulars are restricted to one location at a time. Furthermore, universals can be fully present at different times, which is why they are sometimes referred to as repeatables in contrast to non-repeatable particulars. The so-called problem of universals is the problem to explain how different things can agree in their features, e.g. how a tomato and a strawberry can both be red. Realists about universals believe that there are universals. They can solve the problem of universals by explaining the commonality through a universal shared by both entities. Realists are divided among themselves as to whether universals can exist independently of being exemplified by something (“ante res”) or not (“in rebus”). Nominalists, on the other hand, deny that there are universals. They have to resort to other notions to explain how a feature can be common to several entities, for example, by positing either fundamental resemblance-relations between the entities (resemblance nominalism) or a shared membership to a common natural class (class nominalism).
Abstract and concrete
Many philosophers agree that there is an exclusive and exhaustive distinction between concrete objects and abstract objects. Some philosophers consider this to be the most general division of being. Examples of concrete objects include plants, human beings and planets while things like numbers, sets and propositions are abstract objects. But despite the general agreement concerning the paradigm cases, there is less consensus as to what the characteristic marks of concreteness and abstractness are. Popular suggestions include defining the distinction in terms of the difference between (1) existence inside or outside space-time, (2) having causes and effects or not and (3) having contingent or necessary existence.
An entity ontologically depends on another entity if the first entity can’t exist without the second entity. Ontologically independent entities, on the other hand, can exist all by themselves. For example, the surface of an apple can’t exist without the apple and so depends on it ontologically. Entities often characterized as ontologically dependent include properties, which depend on their bearers, and boundaries, which depend on the entity they demarcate from its surroundings. As these examples suggest, ontological dependence is to be distinguished from causal dependence, in which an effect depends for its existence on a cause. It is often important to draw a distinction between two types of ontological dependence: rigid and generic. Rigid dependence concerns the dependence on one specific entity, as the surface of an apple depends on its specific apple. Generic dependence, on the other hand, involves a weaker form of dependence, on merely a certain type of entity. For example, electricity generically depends on there being charged particles, but it doesn’t depend on any specific charged particle. Dependence-relations are relevant to ontology since it is often held that ontologically dependent entities have a less robust form of being. This way a hierarchy is introduced into the world that brings with it the distinction between more and less fundamental entities.
Identity is a basic ontological concept that is often expressed by the word “same”. It is important to distinguish between qualitative identity and numerical identity. For example, consider two children with identical bicycles engaged in a race while their mother is watching. The two children have the same bicycle in one sense (qualitative identity) and the same mother in another sense (numerical identity). Two qualitatively identical things are often said to be indiscernible. The two senses of identity are linked by two principles: the principle of indiscernibility of identicals, which holds that numerical identity entails qualitative identity, and the principle of identity of indiscernibles, which states that qualitative identity entails numerical identity. Of these two principles, only the former is generally accepted while the latter remains controversial.
Modality concerns the concepts of possibility, actuality and necessity. In contemporary discourse, these concepts are often defined in terms of possible worlds. A possible world is a complete way how things could have been. The actual world is one possible world among others: things could have been different than they actually are. A proposition is possibly true if there is at least one possible world in which it is true; it is necessarily true if it is true in all possible worlds. Actualists and possibilists disagree on the ontological status of possible worlds. Actualists hold that reality is at its core actual and that possible worlds should be understood in terms of actual entities, for example, as fictions or as sets of sentences. Possibilists, on the other hand, assign to possible worlds the same fundamental ontological status as to the actual world. This is a form of modal realism, holding that reality has irreducibly modal features. Another important issue in this field concerns the distinction between contingent and necessary beings. Contingent beings are beings whose existence is possible but not necessary. Necessary beings, on the other hand, couldn’t have failed to exist. It has been suggested that this distinction is the highest division of being.
The category of substances has played a central role in many ontological theories throughout the history of philosophy. “Substance” is a technical term within philosophy not to be confused with the more common usage in the sense of chemical substances like gold or sulfur. Various definitions have been given but among the most common features ascribed to substances in the philosophical sense is that they are particulars that are ontologically independent: they are able to exist all by themselves. Being ontologically independent, substances can play the role of fundamental entities in the ontological hierarchy. If ‘ontological independence’ is defined as including causal independence then only self-caused entities, like Spinoza’s God, can be substances. With a specifically ontological definition of ‘independence’, many everyday objects like books or cats may qualify as substances. Another defining feature often attributed to substances is their ability to undergo changes. Changes involve something existing before, during and after the change. They can be described in terms of a persisting substance gaining or losing properties, or of matter changing its form. From this perspective, the ripening of a tomato may be described as a change in which the tomato loses its greenness and gains its redness. It is sometimes held that a substance can have a property in two ways: essentially and accidentally. A substances can survive a change of accidental properties but it cannot lose its essential properties, which constitute its nature.