Ontology

=== Reality and actuality ===
According to [[Alfred North Whitehead|Alfred N. Whitehead]], for ontology, it is useful to distinguish the terms 'reality' and 'actuality'. In this view, an 'actual entity' has a philosophical status of fundamental ontological priority, while a 'real entity' is one which may be actual, or may derive its reality from its logical relation to some actual entity or entities. For example, an occasion in the life of Socrates is an actual entity. But Socrates' being a man does not make 'man' an actual entity, because it refers indeterminately to many actual entities, such as several occasions in the life of Socrates, and also to several occasions in the lives of [[Alcibiades]], among others. But the notion of man is real. It derives its reality from its reference to those many actual occasions, each of which is an actual entity. An actual occasion is a concrete entity, while terms such as 'man' are abstractions from many concrete relevant entities.{{Citation needed|date=May 2020}}

According to Whitehead, an actual entity must earn its philosophical status of fundamental ontological priority by satisfying several philosophical criteria, as follows:{{Citation needed|date=May 2020}}
* There is no going behind an actual entity, to find something more fundamental in fact or in efficacy. This criterion is to be regarded as expressing an axiom, or postulated distinguished doctrine.
* An actual entity must be completely determinate in the sense that there may be no confusion about its identity that would allow it to be confounded with another actual entity. In this sense an actual entity is completely concrete, with no potential to be something other than itself. It is what it is. It is a source of potentiality for the creation of other actual entities, of which it may be said to be a part cause. Likewise it is the concretion or realization of potentialities of other actual entities which are its partial causes.
* Causation between actual entities is essential to their actuality. Consequently, for Whitehead, each actual entity has its distinct and definite extension in physical [[Minkowski space]], and so is uniquely identifiable. A description in Minkowski space supports descriptions in time and space for particular observers.
* It is part of the aim of the philosophy of an ontology such as Whitehead's that the actual entities should be all alike, ''qua'' actual entities; they should all satisfy a single definite set of well stated ontological criteria of actuality.

Whitehead proposed that his notion of an occasion of experience satisfies the criteria for its status as the philosophically preferred definition of an actual entity. From a purely logical point of view, each occasion of experience has in full measure the characters of both objective and subjective reality. Subjectivity and objectivity refer to different aspects of an occasion of experience, and in no way do they exclude each other.<ref>[[Alfred North Whitehead|Whitehead, Alfred N.]] 1929. ''Process and Reality''. Cambridge: [[Cambridge University Press]]. ''passim''.</ref>

Examples of other philosophical proposals or candidates as actual entities, in this view, are Aristotle's 'substances', Leibniz' monads, and Descartes' ''res verae'', and the more modern 'states of affairs'. Aristotle's substances, such as Socrates, have behind them as more fundamental the 'primary substances', and in this sense do not satisfy Whitehead's criteria. Whitehead is not happy with Leibniz' monads as actual entities because they are "windowless" and do not cause each other. 'States of affairs' are often not closely defined, often without specific mention of extension in physical Minkowski space; they are therefore not necessarily processes of becoming, but may be, as their name suggests, simply static states in some sense. States of affairs are contingent on particulars, and therefore have something behind them.<ref>[[David Malet Armstrong|Armstrong, D. M.]] (1997). ''A World of States of Affairs'', Cambridge University Press, Cambridge, England, {{ISBN|0521580641}}, p. 1.</ref> One summary of the Whiteheadian actual entity is that it is a process of becoming. Another summary, referring to its causal linkage to other actual entities, is that it is "all window", in contrast with Leibniz' windowless monads.{{Citation needed|date=May 2020}}

This view allows philosophical entities other than actual entities to really exist, but not as fundamentally and primarily factual or causally efficacious; they have existence as abstractions, with reality only derived from their reference to actual entities. A Whiteheadian actual entity has a unique and completely definite place and time. Whiteheadian abstractions are not so tightly defined in time and place, and in the extreme, some are timeless and placeless, or 'eternal' entities. All abstractions have logical or conceptual rather than efficacious existence; their lack of definite time does not make them unreal if they refer to actual entities. Whitehead calls this 'the ontological principle'.<ref>{{Cite journal |last=Haring |first=Ellen S. |date=1962 |title=The Ontological Principle |url=https://www.jstor.org/stable/20123918 |journal=The Review of Metaphysics |volume=16 |issue=1 |pages=3–13 |jstor=20123918 |issn=0034-6632}}</ref>