Essence

I

Introduction

Essence, the property or properties an object must have if it is to be what it is. In addition, if being human is the essence of Socrates, it is then a necessary truth about Socrates that he is human.

The thesis that objects have essences might be motivated as follows. It seems plausible to suppose that an object might not have had some of the properties it actually has. For example, Socrates might not have been executed by the Athenians in 399 bc; he might have died peacefully in his sleep a few years later. However, there seems to be a limit to the properties Socrates could have failed to have while remaining Socrates. Suppose one suggested that Socrates could have been a giraffe rather than a human being. At this point most people will agree that we have simply ceased to talk about a genuine possibility for the historical Socrates. The historical Socrates—that very individual—could not have been anything other than human. Having been human, therefore, unlike having been executed in 399 bc, is part of Socrates's essence.

The essence of an object is often taken to constitute its identity, that is, what makes the object what it is. Its essence may consist in membership of a natural kind, as in the claim that Socrates is essentially human. Alternatively, some have supposed that each object has a unique individual essence. A special, but controversial, case of individual essence is called a “haecceity”, which is the property an object has of being that very object. Clearly, if there are haecceities, they are properties an object could not have lacked.

II

Aristotle and Locke

For Aristotle, the definition of something states its essence. A scientific understanding of something is achieved only once one has grasped its essence. Aristotle identifies an object's essence with its substantial form: this is what makes the object what it is. For Aristotle, an object's essence is the kind of thing it is: so, the essence of Socrates is to be human; the essence of a house is to be a shelter for people and goods.

The close connection evident in Aristotle's thought between essence, definition, and the means by which we identify something as a member of a kind was challenged by John Locke. Locke distinguished between the “real essence” of an object, which he identified as the internal constitution of its underlying parts, and its “nominal essence”. Its nominal essence is the idea we have in our minds corresponding to the name of the object; this idea is a list, more or less complete, of its known sensible qualities. Since the real essence of an object, according to Locke, is unknown to us, the criteria by which we identify an object are divorced from its underlying nature.

III

Essence in More Recent Philosophy

In recent philosophy, discussion of essence has concentrated on the question of what kind of necessity is involved in the claim that an essential property is a property an object must have. Willard Van Orman Quine argued against essences, contending that what makes something necessary is not some feature of the object concerned, but rather some feature of the way we describe the object. For example, the number nine may be referred to by the numeral “9” or, since there are nine planets, by the phrase “the number of the planets”. However, while the sentence “9 is necessarily greater than seven” is true, the sentence “the number of the planets is necessarily greater than seven” is false, since there might have been fewer planets than seven. The necessity, Quine argues, is a function of the way we describe the object concerned.

Against Quine, the American philosopher Saul Kripke argued that the example turns on a feature of descriptions such as “the number of the planets”. Kripke calls such a description a “weak designator”: it does not designate the same object in all possible worlds, that is, in all possible conditions of the actual world. By contrast, natural kind terms and proper names are “rigid designators”. For example, the term “water” designates a substance which is H ₂O in all possible worlds. Water is thus necessarily H₂O and this fact is independent of the way we describe water. For Kripke, therefore, natural kinds such as water have empirically discoverable essences. Kripke also argues in defence of individual essences, which he ties to the necessity of something's origins, for example, of an individual person's having come from a particular fertilized egg and sperm consisting of a particular set of atoms.

Modern philosophical discussion of essence is embedded in discussion of a cluster of related problems: these concern modality, theories of naming and reference, natural kinds, and laws of nature.

See also Metaphysics; Nominalism; Phenomenology.