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Ontology is the most general science or study of Being, Existence, or Reality. An informal use of the term signifies what, in general terms, a philosopher considers the world to contain. Thus it is said that Descartes proposed a dualist ontology, or that there were no gods in d'Holbach's ontology. But in its more formal meaning, ontology is the aspect of metaphysics aiming to characterize Reality by identifying all its essential categories and setting forth the relations among them.

Being Qua Being

Existence, as the most comprehensive category of all, should embrace members with the least in common. Nevertheless, Western philosophy long sought some substantive common content present in anything just in virtue of its existence. The history of these attempts to identify the common character of being qua being is not encouraging.

In The Sophist, Plato's Eleatic Stranger proposes that a role in the world's causal network is the necessary and sufficient condition for existence, that "Power is the mark of Being." This idea has had some currency in the twentieth century, particularly in the work of David Lewis (1986) and D. M. Armstrong (1978, 1989, 1997). This Eleatic principle is an attractive test for reality in the natural world, for whatever is real in nature should be able to make a difference. It might be necessary to weaken the requirement and admit a passive space-time that provides the arena within which the active beings exert themselves. Even so, the Eleatic principle seems to be at best a contingent aspect of the world because there seems to be no impossibility involved in the idea of a completely inert being. It also begs the question against abstract entities such as numbers, or geometric points, or sets, which, if they exist, lie outside the causal nexus.

For Samuel Alexander (1920), to be is to be the exclusive occupant of a volume of space-time. This rules out not only abstract entities, but even a field theory of the natural world, for force fields occupy regions of space-time, yet do not exclude one another.

J. M. E. McTaggart (19211927) argued that the mark of being is to stand in a determining correspondence with all of one's infinite parts. A determining correspondence ensures that from a sufficient description of anything, a sufficient description of any of its parts can be derived. This requirement implies that space, the natural world, and most of the contents of minds are unreal. From this consequence the conclusion to be drawn is that McTaggart's proposed mark of being is excessively demanding.

The problem of a substantive content for being qua being is reflected in the idiosyncratic behavior of the verb "to exist." Consider singular negatives: "Aristotle does not speak Spanish" is true because the predicate "does not speak Spanish" applies to the item referred to by the subject term. But "Pegasus does not exist" cannot be true because its predicate applies to the item referred to by the subject term. If the subject term refers to anything, that item exists, which would make the whole statement false.

Kant famously declared that existence is not a property, and this view has become widely accepted. The modern logic that descends from Gottlob Frege and the Principia Mathematica (19101913) of Alfred North Whitehead and Bertrand Russell replaces all expressions using "exists" with others using "There are." Thus, "Lions exist" becomes "There are lions," while "Dragons do not exist" becomes "There are no dragons."

In technical terms, this process replaces any existence claim with one using a quantifier ranging over a domain (the world), so that to exist becomes a matter not of possessing the special property existence, but of possessing some other, ordinary, properties. The determination to restate all claims to existence or nonexistence with "There are " and "There are no " is expressed in W. V. Quine's dictum: "To be is to be the value of a variable."

If existence is not a property, it cannot be a perfection. This undercuts those versions of the ontological argument for the existence of God that rely on existence being among the perfections. A recent response has been to argue that, even if existence is not a property, necessary existence is (Plantinga 1974, 1975; van Inwagen 1993).

Reality and Actuality

Is existence all there is, or should we recognize categories even broader that that of Being? In Plato, and even earlier, is to be found the distinction between Reality (What is) and Appearance (What is not nothing, yet only seems to Be). Aristotle distinguishes the fully existent (Being), from that which is still in formation (Becoming). These distinctions are perhaps best seen as advocating different grades of reality within the one category of Being.

Aristotle also distinguishes the fully Real (Act) from that which may be (Potency). This distinction is the forerunner of a strong strand in ontology that recognizes possible worlds in addition to the actual world, the one we inhabit. In the Neoplatonists, and again in Alexius Meinong, the realm of the existent is augmented by that of the subsistent, which encompasses what does not exist although it might have done so, such as golden mountains.

A full-scale ontology of this kind, in which the realm of Essence is wider than that of Existence, was presented by James K. Feibleman in 1951. In the work of Richard Sylvan (1980), this is extended even further. In Sylvan's system, the individual variables range over not only the actual and the possible, but the impossible as well.

possible worlds

Gottfried Wilhelm Leibniz was the first to make systematic use of the idea that all the possibilities can be regarded as forming worldseach a complete internally consistent realm that may combine some elements matching the actual world with others in which it differs. The actual world is one of the possible worlds, distinguished from all others by the fact that none of its elements is merely possible. If one is able to refer to possible worlds, it is easy to define necessary beings, otherwise so difficult to characterize, as those present in all possible worlds (see below).

modal realism

Possible worlds make available explanations of causal powers, of counterfactual conditionals, of unexercised dispositions, and of real uninstantiated properties. Such advantages led David Lewis (1986) to embrace modal realism, which affirms the literal reality of all possible worlds.

Other philosophers, while appreciating these advantages, have balked at the apparently infinite expansion of the ontology that this requires. This has led to accounts of ersatz possible worlds: Rudolf Carnap and others have proposed that a possible world is a maximally consistent set of sentences. Armstrong and others have developed Wittgenstein's idea that a possible world is a nonactual recombination of the elements of this world. Peter Lopston (2001) advances a reductive realism, which expands the kind of property assigned in the actual world to include might-have-had features. The success of these approaches is subject to continuing controversy.

many worlds in quantum theory

The notion that the world we live in is not the only one has also been canvassed recently in the interpretation of some otherwise baffling paradoxes in quantum physics. On these accounts the world is not a single unified entity, but one subject to continual bifurcation, a process that generates an ever-increasing number of worlds. Many-world views of this kind are in an important way different from modal realism: all these quantum worlds are supposed to be actual but mutually inaccessible.

The Categories of Being

The principal task of ontology is to furnish an inventory of the categories, the most general divisions of Reality. The most important of these are:


An individual or particular substance is an object, a thing in its own right. Common everyday things, such as bricks and bedsteads, provide a model for the category of substance. Substances are required to have several basic features, although it is not clear that these features are compatible with one another.

Particularity and individuality

A substance is both a particular and an individual; not just some duck or other, but this very duck. An object is of the kind it is (a duck) on account of its properties. But if these properties are universals, shared by many particulars, they cannot themselves confer particularity. Some philosophers, most notoriously Locke, proposed a constituent of substances that would perform this role, a substratum that would confer both particularity and individuality. A substratum would be a bare particular, an item inherently particular and individual, yet without any other feature. It is difficult to see how such bare particulars could be distinguished from one another, but if bare particulars are all exactly alike, how could any one of them individualize its own substance? More generally, bare particulars conflict with Aristotle's dictum that the minimum of being, the least thing there can be, is a "this-such," a particular having a property.

Another proposal is that substances are individuated by their location. Locationsspace-time points and regionsare themselves unique particulars; if they can have primitive particularity, that raises the question why other particulars require a substratum or other particularizer. There are other difficulties with location also: Location will not individuate force fields or other physical entities that do not monopolize their space. It fails also for any items of an immaterial kind.

Either individualityand hence particularityare primitive, or there are bare particulars, or each substance has a special property, known as haecceity or thisness, which can bestow particularity and individuality on its bearer. For a discussion see chapter fifteen of John Heil's From an Ontological Point of View (2003).


Individual substances must be distinguished from compounds, so a single substance must be indivisible, in the sense that it has no parts that are themselves substances. This disqualifies ordinary things as individual substances. This simplicity requirement is much emphasized in Aquinas's doctrine of God. It leads in Leibniz to the monadology, and in Roger Joseph Boscovich to the doctrine of material points.


Substances are distinguished from their properties by a capacity to persist, that is, to retain their identity through at least some changes. A fire truck can change in color, yet remain the fire truck it always has been. The ordinary compound substances of everyday life have some persistence, but cannot survive all changes. A fire truck dismantled and scrapped is no longer a fire truck. Complete persistence belongs only to the fundamental substances.


Any substance could be the only thing in existence. If this independence is interpreted causally, no ordinary object is a substance, for they are all brought into being, and hence depend for their existence on their causes. Space-time and its fields might qualify, yet even these depend, in theistic systems, on the creative activity of God. So in Thomism, God is the substance par excellence, but the natural world includes created substances, dependent on God, but otherwise existent in their own right. Spinoza, insisting on absolute independence, concluded that there can be only one substance, the all-embracing totality, God-or-Nature.

If one takes the independence of substances in a logical, rather than a causal sense, a substance is anything that, in principle, could stand alone. This was David Hume's requirement, and anything meeting it is a Humean substance. For compounds, the requirement is that the thing, including all its parts, could exist alone. This requirement is much less rigorous than causal independence and requires no persistence.

No-substance theories

There have been attempts to dispense with substances. Russell has proposed that an ordinary concrete object is no more than a bundle of all its properties. There is always an issue over what it is that binds the bundle. Moreover, as the properties are universals, this theory implies that no two things can be exactly alike.

In Donald Williams's version of the bundle theory (1966), the properties are particular instances or tropes (see below). This avoids any problem with the possibility of there being two exactly resembling objects, but it requires that all members of the bundle be "compresent"all at the same place in space-time. There are difficulties in treating a space-time location as just one further trope in the bundle, but if it is given special treatment it becomes a substantializing substratum.

Russell also advocated an event ontology as a no-substance view. He used "event" for the occurrence of a property at a place and a time; such events are not happenings, but states of affairs (see below). He proposed that ordinary substances, and their more fundamental parts, are sequences of clusters of such events.

The basic elements in these ontologies may not be simple or indivisible, and they lack persistence. Nevertheless, these states of affairs or events are Humean substances. Indeed, unless there is nothing at all, something must be a Humean substance, and in that sense, any no substance theory must fail.

properties and relations

Properties are the intrinsic features or characteristics of things, which belong to them considered singly. Relations, involving two or more terms, are the ways in which things stand to one another. In many respects, properties and relations can be treated together.

Properties as universals

Properties are usually thought of as universals that can characterize indefinitely many instances. There is but one Eiffel Tower, but the tower's height, weight, and iron constitution are features it has in common with many other things. The Problem of Universals is the problem of explaining how any one real entity could possibly exist, fully and completely, in many different instances. This problem has attracted three different proposed solutions: nominalism, conceptualism, and realism. Nominalism and conceptualism both deny that properties are genuinely universal. According to nominalism, the only element common to all iron things is that they can all be described using the predicate "iron," or all are members of the class iron things, or all resemble some typical iron objects. According to conceptualism, the universal element consists in an impulse of our minds to group several things together. These reductive theories have had adherents since the time of Plato and were particularly prevalent among the British Empiricists and their descendents. Nominalism and conceptualism were explicitly challenged by Russell in Problems of Philosophy (1912). The most thorough case against such views is presented in D. M. Armstrong, Universals and Scientific Realism (1978).

Realism regarding universals is at least as old as Plato. His theory of Forms presents a thoroughgoing realism that accords to genuine properties both a real existence, in a realm of their own, and a status superior to any this-worldly instantiations of them there may be. The Forms exist ante rem that is, whether or not they are instantiated. The traditional account of Aristotle ascribes to him a modified realism, according to which properties are real, and universal, but can exist only in rebus, as the properties of concrete instances. Here one encounters again his view that the least that is "apt for being" is a this-such, a union of particular with universal.

Realism has always faced two principal objections. First, that it is uneconomical, especially in its Platonist form. The question of economy is a current issue in the philosophy of science, as it at least appears that our best physical and chemical theories involve uninstantiated properties. The second objection is that it can provide no coherent account of the link between a property and the substance that bears it, the inherence relation. Inherence cannot be a normal relation, for then it is just one further universal standing in need of an inherence link to its terms, the substance and the original property. But if it is not a relation in the ordinary sense, what is it? The problem with inherence lends support to versions of realism in which properties are particulars.

Properties as particulars

Even if the property iron is universal, the particular case of being iron that occurs in the Eiffel Tower belongs to the tower alone and is as particular as the tower itself. Trope theory, as developed first by Donald Williams, treats the instance not as a dependent entity arising from the instantiation of a universal, but as a Humean substance in its own right.

When this approach is coupled with a bundle or compresence account of ordinary many-featured substances, the problem of any inherence relation disappears. There is a further significant economy, for there is no need for a separate category of substance. These possibilities are explored further in Keith Campbell's book Abstract Particulars (1990).


When Russell reanimated the realism debate he accorded to relations a status fully equal to that of inherent properties. Indeed, it was his reflections on the role of relations in the foundations of mathematics and of logic that led him to his realism. Armstrong's realism takes the same form.

There is, nevertheless, a long tradition that accords primacy to the intrinsic properties. Aristotle held that relations are "the least of the things that are"; Hobbes and others held that the existence of relations depends on a mental act of comparison; and Leibniz's view was that every relation has its foundation in an intrinsic feature of one or both of its terms. This reductive program is expounded in Campbell (1990).

Relations do seem to be dependent in the sense that they must have substances as their terms, and these substances must have intrinsic properties. So unless there are intrinsic properties there can be no relations, but not vice versa. Bundle theories of ordinary things concern only the intrinsic properties. To include relations in the bundles leads to problems over where to assign the relations, and this in turn induces a tendency towards a monism such as Francis Herbert Bradley's, in which ordinary substances are absorbed into a single all-embracing totality.


Some properties, such as square, seem to belong to how an object is. Others, such as being a solvent, seem to refer to what an object can do. This is the distinction between categorical and dispositional properties. One line of thought takes up the Eleatic principle, and identifies real properties as those that confer on their bearer a disposition to act or to be acted upon. Such dispositions are powers ; a metaphysic of powers is set forth in George Molnar's Powers (2003) and in Brian Ellis's Scientific Essentialism (2001).


Substance and property are basic categories. In combination, they can provide a richer ontology.

States of affairs

A basic state of affairs consists in a particular having a property, or in two (or more) particulars standing in a relation. A single property inhering in a single particular is a minimal "this-such." Wittgenstein's Tractatus Logico-Philosophicus (1921) presented an ontology in which the world is composed of minimal relational states of affairs: those that actually obtain being facts, those merely possible being the remaining states of affairs. These themesthat the basic categories only ever occur in combination, and that these combinations constitute realityare taken up in D. M. Armstrong's A World of States of Affairs (1997).

Events and processes

A state of affairs is static. To account for the dynamic aspects of the world requires an account of change. This can be done by using sequences of states of affairs: stability consists in successive states of affairs closely resembling one another, whereas change consists in the states of affairs at one time being replaced by others systematically different. An event is a single change, involving a pair of states of affairs; a process is a more complex series of events.

Whitehead, in Process and Reality (1929) accorded priority to the dynamic; all apparently persisting substances are actually slowly evolving processes. The status of space-time is still controversial. It may be a Humean substance; however, some accounts of matter assign it a place as a process, a sequence of complex, changing relations between particulars.

Abstract Objects

Human thought, particularly in mathematics and logic, seems to involve entities that have no apparent place in the natural spatiotemporal world, and no causal role. To admit such items challenges the principle of economy, yet successful reductions are difficult to accomplish.

numbers and sets

Because all numbers can be represented in set theory, there is no need to admit both sets and numbers. Russell had proposed to eliminate sets in favor of propositional functions, but this proved impossible for more than a fragment of mathematics (Goodman and Quine 1947, Quine 1969). Because the variables of set theory have sets as their values, and to be is to be the value of a variable, we are committed to their realitythis is Platonism about sets and numbers. The most important work in attempting to avoid Platonism is Hartry Field's (1980, 1989).

geometrical objects

Unlike anything in the natural world, the objects of geometryEuclidian cubes, for exampleare thought of as perfect, changeless, timeless, and without any physical causal powers. Moreover, there are geometries, and corresponding geometrical objects, with many more dimensions than this world has. A geometrical space can be divided and subdivided into an infinity of different shapes of different sizes. Platonism in geometry thus involves an infinite expansion in ontology.

One approach to this issue is to consider geometrical objects as abstracted objects, that is, objects taken from a context. On this view, every cube is just a particular spatial fragment of space-time and every triangle a fragment of one of space-time's spatial surfaces. One problem with this is that not all shapes will be available. If our space-time is nowhere perfectly Euclidean, there will be no real Euclidean cubes. We can treat these nonexistent objects as imaginary variations on the actually existing ones, and geometries that quantify over such things, as not literally true.


The philosophy of logic makes reference to propositions, operators, functions, and inferences. These are abstract entities, related to reasoning in much the same way as numbers are related to counting and measuring. The problems and prospects of a reductive treatment of them are also parallel.

Necessary Beings

Ordinary things are usually held to exist contingently; that is, they do exist, but might not have. Had our world's initial conditions or laws of nature been different, there would have been a different group of contingent beings. But some things seem to be immune from the vagaries of cause and chance; being outside the causal net, they cannot be brought into being and cannot be destroyed. These are "necessary beings." If Platonism is correct regarding any of the abstract objects, these will be necessary beings, even, paradoxically, the null class.

For Aristotle, anything that exists through an infinite time is necessary because he held that over infinite time every possibility would at some point be actualized. For Plotinus, any divine being would be outside time, and as such could not change, could not cease to exist, and thus would be A necessary being. For Aquinas, God's necessity derives from his simplicity: God's essence and his existence are identical; in this way he is a kind of being that must exist. For Spinoza, every genuine substance is causa sui, containing within itself the sufficient explanation for its own being, and thus it can guarantee its own existence under all possible conditions.

Duns Scotus, then Descartes, linked necessary being with logic: A necessary being is one, the denial of whose existence would be self-contradictory. "Real"i.e., existing"beans do not exist" is a self-contradiction, but only trivially because existence has been inserted into the definition of the subject. This does not make beans necessary beings. If existence is not inserted into the subject term's definition, it is doubtful whether any denial of existence would be a self-contradiction. The best discussion of necessary being is in Alvin Plantinga (1974, 1975).

See also Metaphysics.


Adams, R. M. "Primitive Thisness and Primitive Identity." The Journal of Philosophy 76 (1979): 526.

Alexander, Samuel. Space, Time, and Deity: The Gifford Lectures at Glasgow. 2 vols. London: Macmillan, 1920.

Armstrong, D. M. A Combinatorial Theory of Possibility. Cambridge, U.K.: Cambridge University Press, 1989.

Armstrong, D. M. Universals and Scientific Realism. 2 vols. Cambridge, U.K.: Cambridge University Press, 1978.

Armstrong, D. M. A World of States of Affairs. Cambridge, U.K.: Cambridge University Press, 1997.

Campbell, Keith. Abstract Particulars. Oxford: Blackwell, 1990.

Ellis, Brian. Scientific Essentialism. Cambridge, U.K.: Cambridge University Press, 2001.

Feibleman, James K. Ontology. Baltimore: Johns Hopkins Press, 1951.

Field, Hartry. Realism, Mathematics and Modality. Oxford: Blackwell, 1989.

Field, Hartry. Science without Numbers: A Defence of Nominalism. Oxford: Blackwell, 1980.

Forbes, Graeme. The Metaphysics of Modality. Oxford: Clarendon Press, 1985.

Goodman, N., and W. V. Quine. "Steps Towards a Constructive Nominalism." Journal of Symbolic Logic 12 (1947): 105122.

Heil, John. From an Ontological Point of View. Oxford: Clarendon Press, 2003.

Lewis, David K. On the Plurality of Worlds. Oxford: Blackwell, 1986.

Loptson, Peter. Reality: Fundamental Topics in Metaphysics. Toronto: University of Toronto Press, 2001.

McTaggart, J. M. E. The Nature of Existence. 2 vols. Cambridge, U.K.: Cambridge University Press, 19211927.

Molnar, George. Powers: A Study in Metaphysics. New York: Oxford University Press, 2003.

Plantinga, Alvin. God, Freedom, and Evil. London: Allen and Unwin, 1975.

Plantinga, Alvin. The Nature of Necessity. Oxford: Clarendon Press, 1974.

Quine, W. V. From a Logical Point of View: 9 Logico-Philosophical Essays. 2nd ed. Cambridge, MA: Harvard University Press, 1961.

Quine, W. V. Set Theory and Its Logic. Cambridge, MA: Belknap Press of Harvard University, 1969.

Russell, Bertrand. The Analysis of Matter. London: Kegan Paul, Trench and Trubner, 1927. Event ontology.

Russell, Bertrand. An Inquiry into Meaning and Truth. London: Allen and Unwin, 1940. Substances as bundles of universals.

Russell, Bertrand. The Problems of Philosophy. London: Oxford University Press, 1912. Realism about universals

Sylvan, Richard. Exploring Meinong's Jungle and Beyond. Canberra: Australian National University, 1980.

Van Inwagen, Peter. Metaphysics. Boulder, CO: Westview Press, 1993.

Whitehead, A. N. Process and Reality: An Essay in Cosmology. Cambridge, U.K.: Cambridge University Press, 1929.

Williams, Donald C. Principles of Empirical Realism: Philosophical Essays. Springfield, IL: Thomas, 1966.

Wittgenstein, Ludwig. Tractatus Logico-Philosophicus. London: Routledge and Kegan Paul, 1921.

Keith Campbell (2005)

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From the Greek ontos and logos, ontology refers to the investigation of being as such, or to the science of being as being. It may also consider what it means to be, what sorts of entities are countenanced, and what kinds of ultimate presuppositions or principles are held or obtained. The term "ontology" is usually traced to the early 17th century, but its significance for modern philosophical reflection is rooted in both ancient and medieval speculation about metaphysics. In the 17th century ontology was initially identified as a part of metaphysics, but today "metaphysics" and "ontology" are often used in popular speech as synonyms. This article traces the origin and development of the term from its inception in Aristotle's Metaphysics, its solidification as a single science in the Middle Ages, and its separation from metaphysics proper, under the influence of Wolff, during the modern period. The Wolffian tradition survives in modern philosophical usage and serves to explain the order of many scholastic manuals in which ontology is placed after logic and before tracts on special metaphysics.

Ancient and Medieval Origins . In a series of writings, later classified by Andronicus of Rhodes (c. 50 b.c.) as "the books after the physical ones" (ta biblia meta ta physika ), Aristotle discusses a science of being simply as being and not as some particular class of beings or part of being. Though he acknowledges in the fourth book of the Metaphysics (1003a1003b19) various senses of "being", he claims that there is one primary sense or character by virtue of which these many senses are understood, and that there is some primary science or first philosophy. In the sixth book (1026a1632), Aristotle refers to a first philosophy that is concerned with being as being, but in contrast to physics and mathematics, precisely as the speculative science of what is separate from matter and motion. First philosophy in this context is labeled "theology" inasmuch as the divine would only be present in something of this nature, i.e., some immutable being (ousia akinetos ). Aristotle adds further that this theology would be universal by virtue of the fact that it is first philosophy, i.e., by virtue of its consideration of being in the primary sense.

These references in Aristotle's Metaphysics to a science of being as being and to divine science, to "first philosophy" and to "theology," are not unambiguous, as subsequent thinkers repeatedly recognized. Is Aristotle referring to two distinct sciences or is he employing more than one name for the same science? If the latter, how can both being in general and a particular being be the subject of the same science?

In the 13th century, appropriating Aristotle's threefold division of the speculative sciences (physics, mathematics, and what Aquinas variously calls "first philosophy" or "metaphysics" or "theology"), Aquinas argues that primary being and being in general are the subject of the same science (eadem enim est scientia primi entis et entis communis ) inasmuch as primary being (s) are principles of the others (nam prima entia sunt principia aliorum ; cf. Aquinas' In Boeth. de Trin. 5.1, In 10 meta. 6 and 11, and the Proemium to the latter). Nevertheless, given the potential for ambiguity in Aristotle's writings themselves, medieval philosophers before and after Aquinas debated the subject matter of metaphysics, as evidenced in the first of the questions raised by Duns Scotus regarding Aristotle's Metaphysics, viz., "Whether the subject of metaphysics is being insofar as it is being, as Avicenna posited being, or God and the Intelligences, as posited by the commentator Averroes?" In the 17th century what may be viewed as the equivalent to Avicenna's interpretation of the subject matter of Aristotle's Metaphysics is dubbed "ontology."

Modern Period . R. Göckel in his Lexicon philosophicum (1613) continues the Aristotelian tradition of distinguishing three progressively abstract "contemplative sciences." However, after physics and mathematics, Göckel accepts a further distinction, urged by Pererius, between divine science and the science of being. The former Göckel labels the transnatural science of God and angels, the latter "ontology," i.e., the science of being and transcendence. In another 17th century Lexicon philosophicum, authored by Micraelius and first published in 1653, a general metaphysics, apparently identified with ontology and concerned with being in the most abstract sense, is distinguished from a particular metaphysics which considers the types of beings separate from matter, viz., God, angels, and the departed souls. Also identifying ontology (or "ontosophy") as the study of ens in genere, although in a fashion much closer to Aristotle's descriptions of "first philosophy," is Clauberg in his Elementa philosophiae sive Ontosophia (1647) and in the Prolegomena to his Metaphysica (1656). In Du Hamel's Philosophie vetus et nova (1678) "ontology" is identified as the first or primary sort of metaphysics, the "scientia generalis" concerned with the nature of being itself, its principles, properties, and types. The two kinds of specialized metaphysics, derivative of this ontology, are the study of the causes of physical things (physicae contemplationis caput ) and natural theology.

What these various 17th century thinkers commonly illustrate is a tendency to distinguish ontology from theologya marked departure from the medieval view of metaphysics as a single science. Representing an even more radical departure within this context is Leibniz's tentative classification of ontology within the scientia generalis he outlines in his Introductio ad Encyclopediam arcanam; sive initia et specimina scientiae generalis (1679). Scientia generalis, "the science of the knowable in the universe inasmuch as it is such," is said to include, in addition to logic, gnoseology, and various other arts, "perhaps also ontology or the science of something and nothing, of being and not-being, of a thing and the mode of a thing, of substance and accident" (forte etiam Ontologiam seu scientiam de Aliquo et Nihilo, Ente et Non Ente, Re et modo rei, Substantia et Accidente ). More influential than Leibniz for the modern use of the term "ontology" in general is the work of the systematizer of a Leibnizian metaphysics, Christian Wolff. According to Wolff's Philosophia prima sive ontologia (1729), "Ontology or first philosophy is the science of being in general or insofar as it is being" (Ontologia seu Philosophia prima est scientia entis in genere, seu quatenus ens est ), a metaphysica generalis in contrast to the secondary metaphysicis specialibus : rational psychology, cosmology, and rational theology.

With Wolff, then, the dismemberment of what Aristotle apparently and Aquinas quite clearly construed as a single science (first philosophy, theology, metaphysics) is complete. For Wolff first philosophy is ontology, the study of being as being, and not to be confused with the particular metaphysical discipline of rational theology.

Enlightenment Era . Although sharply critical of Wolff's "dogmatic" metaphysics, Kant expressed appreciation for the "incontestable service" rendered by the clarity of Wolff's delineation of ontology. In the prize essay, "What is the actual progress made by metaphysics since the time of Leibniz and Wolff?" (1791) Kant in fact identifies ontology with transcendental philosophy [see also "The Architectonic of Pure Reason" at the end of the Critique of Pure Reason (1781; 1787)]. Ontology in this sense can be considered a propadeutic to metaphysics and in that sense even a part of metaphysics, where "metaphysics" is precisely understood as the science of progressing from knowledge of the sensible to that of the supersensible.

Ontology is that very science (as part of metaphysics) which constitutes a system of all concepts of understanding and fundamental principles, yet only insofar as the latter concern objects which can be given to the senses and thus can be corroborated by experience.

Wolff's conception of ontology as a science of being as being, apart from particular beings, resembles, at least formally, one of the meanings of "first philosophy" articulated in Aristotle's Metaphysics. By contrast, in Kant's transformation of ontology into a system of categories and principles of sensible, verifiable objects, the echo of the Aristotelian heritage may seem fainter, yet it is no less discernible. Kant's ontology is precisely that system of concepts and principles by virtue of which alone a sensible object can be judged to be. (Also resembling Aristotle's approach to "first philosophy" as well as Aquinas' account of the same, Kant ties this ontology to that which can be said to be in a primary sense, viz., the mode of being sensibly given.)

Not unlike Kant, Hegel employs a Wolffian notion of "ontology" in connection with his own discussion of categories in his "objective logic," constituted by the first half, i.e., the first two books of the Science of Logic. The objective logic is supposed to take the place of ontology in the traditional, i.e., Wolffian metaphysics, "the part of that metaphysics that is supposed to investigate the nature of Ens in general" (cf. the General Division of the Logic in the Introduction to Hegel's Science of Logic ).

Scholastic Tradition . Towards the end of the 19th century and even up to the middle of the 20th century several authors in the scholastic tradition continue to determine the subject matter of ontology in terms of (sometimes critically refined) medieval and Aristotelian accounts of the degrees of abstraction. These writers also generally employ Wolff's terminological identification of "metaphysica generalis" and "ontology." See, for example, the opening page of Carolo Frick's Ontologia sive Metaphysica Generalis (1894): "Metaphysica generalis seu ontologia definitur: scientia rerum, prouti sub rationibus maxime abstractis et hinc communibus exhibentur" or van steenberghen's Ontology (1946). The aim of Cardinal Mercier's Metaphysique generale ou ontologie (1910) is a demonstration of the sort of interpretation of metaphysics found in Aquinas. "We will show why the science which has the divine being for its object does not differ formally from that which treats of being in general."

Contemporary Phenomenology . In Husserl's Ideas for a Pure Phenomenology and Phenomenological Philosophy (1913) he argues that every factual science has theoretical foundations in pure sciences of essential being. Husserl labels these sciences of essences "ontologies" and distinguishes formal ontologies concerned with the essence of objectivity in general from regional or material ontologies concerned with regional essences, those ultimate and concrete (in the sense of selfsustaining) generic unities in a hierarchy of essences, such as nature, human being, history. Formal ontology here corresponds to what Husserl in his Logical Investigations (1901), following Meinong, called "a pure (apriori) theory of objects as such," the study of formal, objective categories (e.g., whole and part, genus and species), the correlates of categories of meaning (e.g., proposition, truth). In Formal and Transcendental Logic (1929) formal ontology is described as "a science of possible objects purely as possible" and thus as a theory of science by way of contrast with the correlative, thematic concern of formal logic for judgments alone. Although the aims and specifications are quite distinct, Husserl's "formal ontology" as the pure science of essences in the sense of possible objectivities bears a certain (and acknowledged) affinity to Kant's conception of ontology.

Perhaps the thinker most identified with ontology in the 20th century was Martin Heidegger (17:284b) who claimed indeed that "phenomenology, taken in terms of its content, is the science of the being of the particular being (Sein des Seienden )ontology" and that "ontology is only possible as phenomenology." This identification of ontology and phenomenology proposed by Heidegger in Being and Time (1927) departs at once from Husserl's pure science of essences as well as from traditional ontologies in the history of Western philosophy. Precisely because they are rooted in largely unquestioned, pre-ontological modes of human existence, traditional interpretations of what it means to be take their bearings from theoretical inquiries into particular beings, thereby conflating quite distinctive ways of being (for example, the diverse modes of being proper to things, tools, theoretical objects, humans) and reducing being (or, literally, the sense of 'to be') to some particular sort of being. In Heidegger's telling if dramatic expression, traditional ontology betrays the forgottenness of being (Seinsvergessenheit ). Posing the question of being at all accordingly requires the destruction of the traditional content of ontology by way of a fundamental ontology, that is, an interpretation of the fundamental structures of human existence as regards its own most intimate and everyday ways of being; in short, its being-in-the-world as such. The question of being remains the aim of this fundamental ontology, but precisely by way of opening up the horizon "in which something such as being in general becomes understandable," i.e., "the clarification of the possibility of the understanding of being in general, which belongs to the constitution of the particular being we call the human existent or being-there (Dasein )." Within this horizon time (though not the derivative, putatively endless time of clocks and measurement) discloses itself as the meaning of being.

Following World War II Heidegger began to turn from this phenomenological project of a fundamental ontology with its apparent pretensions to a scientific interpretation of what it means to be. Without denying the necessity of having gone down that path, Heidegger sought to bring into play a kind of thinking, more rigorous than science, in which what it means to be announces itself. In Heidegger's later thinking, then, "ontology" (and its synonyms in his early writings "phenomenology," "hermeneutics") was no longer part of his vocabulary for posing the question of beingnor, in his estimation, can it. "The question of the essence of being dies away, if it does not give up the language of metaphysics, since the metaphysical representing prevents it from thinking the question of the essence of being" (On the Question of Being 1955).

Linguistic Analysts . For other philosophers of the 20th century, especially those concerned with the development of logical languages and the foundations of the sciences, "ontology" signified a confused or at best irrelevant consideration. Thus, in "Logic without Ontology"(1944) Ernest Nagel urged a purely operational or contextual account of the role of logico-mathematical disciplines in inquiry, thereby effectively dismissing as "gratuitous and irrelevant" interpretations of their "ultimate meaning" or calls for the necessity of some "a priori insight into the most pervasive structure of things." So also in "Empiricism, Semantics, and Ontology"(1950) Rudolf Carnap distinguished questions of existence internal to a linguistic framework and thus answerable by logical or empirical methods from external questions "concerning the existence or reality of the system of entities as a whole. " The latter sorts of questions of existence cannot be answered because they are framed in the wrong way, that is to say, they are incapable of theoretical resolution because they lie outside the theoretical framework itself. The question as to what sort of things a language will refer to is not a theoretical, but a practical question.

For those who want to develop or use semantical methods, the decisive question is not the alleged ontological question of the existence of abstract entities but rather the question whether the use of abstract linguistic forms or, in technical terms, the use of variables beyond those for things (or phenomenal data) is expedient and fruitful for the purposes for which semantical analyses are made, viz., the analysis, interpretation, clarification, or construction of languages of communication, especially languages of science.

(An albeit strained, but nonetheless quite interesting parallel to Heidegger's criticism of the putatively theoretical approach of traditional ontology is patent, the difference is, of course, that Heidegger did not reduce nontheoretical questioning to matters of belief or pragmatic choice.)

Carnap's influential essay grapples with the problem that even highly formal languages, like those of mathematics and the physical sciences, seem unable to avoid referring to abstract entities such as properties, classes, relations, numbers, and propositions. Accordingly, in addition to the pejorative use just noted, "ontology" has come to designate the sorts of entities or theories about the sorts of entities countenanced by a linguistic system. Questions about the implications of a theory of reference or a semantics are ontological questions. Thus, in Word and Object (1960) Quine spoke of the philosopher's task of "clearing ontological slums." Ontology's job is precisely to scrutinize the uncritical acceptance of such realms as those of physical objects or of classes. By criticizing the tendency on the part of Carnap and others to embrace a sharp boundary between questions of meaning and questions of fact, Quine extended Carnap's own pragmatic approach to ontology (Word and Object was dedicated to Carnap), but in a manner that also called into question his distinction between the internal and external (ontological) questions.

Twentieth-Century Ontologies. Among U.S. and British philosophers during the 20th century there were attempts by thinkers such as Bradley and McTaggart, Whitehead (although he called his epic Process and Reality [1929] "an essay in cosmology"), and Hartshorne to construct ontologies in the tradition of speculative metaphysicians. Perhaps the most sustained such effort is to be found in the works of Paul Weiss. Beginning with Reality in 1938, followed by Modes of Being (1958), Beyond All Appearances (1974), First Considerations (1977), and Privacy (1983), Weiss developed a novel, pluralistic ontology or "study of realities," as he called it. These realities are the actualities (Weiss' "substitute for 'substances' with their supposed adventitious accidents"), finalities ("a plurality of subordinating and subordinated, but ultimately real conditions and sources of contexts which enable particulars to be together"), and the dunamis (an inexhaustible, creative ground, "an indeterminate maw out of which the actualities originate and into which they return").

See Also: philosophy, history of; metaphysics.

[d. o. dahlstrom]

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ONTOLOGY . The word ontology, meaning "discourse about, or study of, being," was introduced into the philosophical vocabulary in the early seventeenth century. The term was originally used as an equivalent for "metaphysics," which Aristotle, in Metaphysics 4.1, had defined precisely as the science that treats "being insofar as it is being." Thus the enterprise of ontology had a long prehistory.

Plato had considered the question of "being" (to on, ousia ), which for him meant the "what" of things as a stable object of certain knowledge. Hence he thought that the term being was properly employed only of the self-identical, changeless, and hence eternal, realm of Formsthat reality, grasped by intellect alone, which is imaged in, but at the same time contrasted with, the mutable realm of "becoming." It was Aristotle, critical of this outright identification of being with the immutable and transcendent Forms, who insisted that the verb "to be" is universally applicable and then proceeded to ask what it means to be (anything). Because, as he frequently observes, "'being' is said in many senses," he denies in effect that the term is used univocally or that it defines an all-inclusive genus. He nevertheless thinks that its primary or focal use is to denote the subject, whether of discourse or of change and action: To be is to be some concrete "thing" (ousia )a changing, individual composite of two correlative principles, form and matter or (in more general terms) actuality and potentiality. The former of these is the active principle of the thing's growth and development (phusis, "nature"), the intelligible identity of it which the mind grasps in knowledge and expresses in judgment, while the latter is the substratum of possibility that allows for change.

This analysis of what "being" means was substantively taken over in the metaphysics of Thomas Aquinas (12251274). Thomas, however, broadened the application of Aristotle's distinction between actuality and potentiality. It included not merely the distinction between the form and the matter that determines the "what" (id quod, "essence") of a thing, but also, and more fundamentally, that between what a thing is and the fact that it is (id quo, "existence"). Essence for Thomas is a potentiality that is brought into "act" only through existing; hence the study of being, in considering the question what it means to be this or that (thing), must focus not merely on what gives a thing ("substance") its identity but also on what accounts for its "being there," its actual existence.

In his treatise First Philosophy or Ontology (1729), however, Christian Wolff (16791754), whose work established the normal modern use of the term, understood ontology as a subdivision of metaphysics: the study of being as a genus ("general metaphysics"), to be distinguished from the subjects of "special metaphysics," that is, theology, psychology, and cosmology. Being, then, was for Wolff a univocal term denoting "what is" in its most universal characteristics. Aristotle's (and Thomas's) insistence on the "many senses" in which "to be" is said recedes into the background: For Wolff, the fundamental principles of being are the laws of noncontradiction and of sufficient reason. Reality is composed of imperceptible simple substances each of whose essences is exhausted by a single clear and distinct idea, and whose existence is accounted for by appeal to the principle of sufficient reason.

This science of generic being, abstract and deductive in form, was rejected by Immanuel Kant (17241804), for whom ontology a term he used very infrequentlycame in effect to be identified with his own transcendental philosophy. This enterprise was concerned not with "things in themselves" but with the subjective preconditions of human knowledgethe forms of sense-perception and the categories of the understandingthrough which the "objects" of the empirical world are constituted as such. The propaedeutic study of being thus became, for Kant, an investigation of the ways in which the subject of knowing "objectifies" the content of experience and so constitutes the "beings" of the phenomenal world. Like Kant, G. W. F. Hegel (17701831) rejected Wolff's "dogmatic" ontology. For him, the study of being took the form of a logic, which explicated the movementfrom simplicity to organic complexity, from "being" to "concept"by which Mind (Geist ) appropriates itself through self-objectification.

In more recent philosophy, the project of ontology, long neglected save in theological circles where traditional scholastic philosophy prevailed, reappeared in the work of Edmund Husserl (18591938). Husserl's search for a sure basis of human knowledge led him to elaborate a phenomenological method that sought to identify and describe "what is" as the world of the "transcendental ego" or "pure consciousness" (as distinct from the empirical self, which is a member of the object-world of scientific inquiry). It was Husserl's student and critic Martin Heidegger (18891976), however, who through his Being and Time most explicitly and influentially revived the project of ontology. For Heidegger, "being" ("to be") is radically distinguished from "beings" ("what there is"). The former is the subject of ontological, the latter of merely "ontic," discourse. The clue to the question of being is, for him, the existent human subject (Dasein ), which is precisely in the act of asking what it means "to be." To grasp what it is "to be" is thus to grasp what is presupposed in the human existent's asking about its being. Ontology is thus again, as for Kant, a transcendental analysisbut not, in this case, of the preconditions of human knowing so much as of the preconditions of human "being-in-the-world."

See Also



Gilson, Étienne. Being and Some Philosophers. Toronto, 1949.

Kung, Guido. Ontology and the Logistic Analysis of Language. New York, 1967.

Martin, Gottfried. Kant's Metaphysics and Theory of Science. Manchester, U.K., 1961.

New Sources

Collier, Andrew. Critical Realism: An Introduction to Roy Bashkar's Philosophy. 1985; reprint, London, 1994.

Snyder, Daniel Howard, and Paul Moser. Divine Hiddenness: New Essays. Cambridge, U.K., 2002.

Weissman, David. A Social Ontology. New Haven, Conn., 2000.

Richard A. Norris (1987)

Revised Bibliography

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Ontology (Gk., ōn, ‘being’, + logos, ‘reflection’). Reflection in philosophy and metaphysics on what truly exists, or on what underlies appearance by way of existent reality. The term was introduced in the 17th cent., when the study of being as being was also called ontosophia. In the continuity of scholasticism, ontology was the term applied to the study of the properties of being as such, in contrast to special metaphysics which studied aspects of being open to experience. W. V. O. Quine made a distinction between ideology and ontology, and between meaning and reference: he argued that what one takes to be existing depends on the values required or allowed by the variables of the language in use, so that there is a necessary relation between language and ontic commitments—hence his claim that ‘to be is to be the value of a variable’. While this might seem to allow virtually any belief to have an ontological correspondent, in fact metaphysical systems (which he called ‘ontic theories’) are tested by their compatibility with science which interacts publicly (and by various other criteria) with the world and universe around us. It then becomes obvious that ontology is intricately related to epistemology (roughly, how do we know what we know?).

Ontologism was a system of philosophy which, applied to theology, claimed that humans know God immediately and directly through natural cognitive abilities: the first act of human cognitive powers is the intuition of God. It was condemned (on the grounds that our knowledge of God can only be analogical) in 1861 and again by Vatican I.

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on·tol·o·gy / änˈtäləjē/ • n. the branch of metaphysics dealing with the nature of being. DERIVATIVES: on·to·log·i·cal / ˌäntəˈläjikəl/ adj. on·to·log·i·cal·ly / ˌäntəˈläjik(ə)lē/ adv. on·tol·o·gist / -jist/ n.

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ontology Any way of understanding the world, or some part of it, must make assumptions (which may be implicit or explicit) about what kinds of things do or can exist in that domain, and what might be their conditions of existence, relations of dependency, and so on. Such an inventory of kinds of being and their relations is an ontology. In this sense, each special science, including sociology, may be said to have its own ontology (for example, persons, institutions, relations, norms, practices, structures, roles, or whatever, depending on the particular sociological theory under consideration). The core of the philosophical project of metaphysics is to provide an ontology of the world as a whole. In some versions of metaphysics this takes the form of an attempt systematically to order the relations between the ontologies of the special sciences.

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Ontology is the study of being, insofar as being is possessed by any kind of entity. Although the term ontologia derives from the early seventeenth century, ontology is as old as philosophy itself. While German mathematician and philosopher Christian Wolff (1679-1754) identified ontology with metaphysica generalis (inquiry into the general categories of being), the relationship between ontology and metaphysics has become less precise. Some believe the two synonymous; others hold that while metaphysics deals with the nature and structure of all possible being, ontology only concerns actually existing beings. Ontological questions permeate the science-religion conversation; for example, what is the ontological status of the divine, and of putative emergent properties (e.g., the mental)?

See also Metaphysics

dennis bielfeldt

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ontology A description of some concepts and their relationships, for the purpose of defining the ideas sufficiently to allow a computer to represent them and reason about them. Thus an agent's ontology specifies the basic building blocks of knowledge that defines what it can perceive and reason about. This is a kind of model and, as such, is very useful to define what agents or learning programs can know and what they can communicate. Ontologies are usually compiled for a particular “domain”, e.g. the domains of wind engineering, medical diagnosis, or office interior navigation, but they are more formal than domain knowledge.

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ontology the branch of metaphysics dealing with the nature of being. Recorded from the early 18th century, the word comes from modern Latin ontologia, from Greek ōn, ont− ‘being’, + the suffix −logy denoting a subject of study or interest.

In philosophy, the ontological argument is the argument that God, being defined as most great or perfect, must exist, since a God who exists is greater than a God who does not.