This article will focus on how different modern philosophers have discussed and articulated the problem of essentialism. This will have implications for our understanding of how essences are to relate to universals. The relevance of these distinctions and issues for the question of how the distinction between sex and gender ought to be understood will quickly become obvious.
What is the relation of natural kinds to universals? Some see natural kind realism as a kind of analogue of realism concerning universals. Others say that natural kinds are a kind of universals and that they are even reducible to universals. Against this position, there are natural kind fundamentalists who argue that natural kinds exists and that they have a basic lace in our metaphysics. Some writers suggest that natural kinds really exist but that it is not necessarily the case that scientists require the “universal” as a kind of irreducible and independent category, by which one could accommodate natural kinds.
“According to David Armstrong (1997, 67–8) “The kinds mark true joints in nature. But it is not clear that we require an independent and irreducible category of universal to accommodate the kinds”. Armstrong’s view is naturalistic, since there are genuine natural divisions; but he is also resistant to realism. If there were natural kinds they would be universals. But the properties shared by all and only the members of a kind will typically be very complex. For example, he considers whether there is some description of human DNA. There may be, but it would be too complex to qualify as a genuine universal. And there is no reason to suppose that this complex universal would do any causal or nomic work. So there is not simply an identity between natural kinds and a subcategory of universals, the natural kind universals (e.g., the universal of being gold, or of being a human)—according to Armstrong’s argument there are no natural kind universals. He does concede that the case is stronger for basic kind universals, such as electronhood, where a few properties (the electron’s mass, charge, and spin) are individually necessary and jointly sufficient for kind membership.”
Some writers argue that natural kinds are complex universals. This is a universal whose parts are themselves universals. For example, the electron contains universals such as charge, spin and mass, which combine to constitute a complex universal. Each entity that embodies the electron-hood also embodies the universals which constitute it, such as mass and charge. Some collections of universals are not natural kinds, however, nor does every clustering of particulars constitute a natural or complex particular. Complex universals are not necessarily as precise as the case of the electron. “Some are vague, and this fact can accommodate the indeterminacy of kind constitution implied by Boyd’s view of the clusters in the case of biological kinds.”
Many writers consider natural kinds to be entities. This is a form of natural kind realism. One writer refers to natural kinds as “substantial universals,” which he sees as constituting “an irreducible ontological category…Hence he is a natural kind fundamentalist.” He notes a distinction between substantial universals, or natural kinds, and non-substantial universals, or ordinary properties. He believes that this distinction
“accounts for the laws of nature in a manner that, while avoiding the problems of a regularity account, may nonetheless do without Armstrong’s second order relation of necessitation, itself a relational universal (Armstrong 1983, 75–110). Consider the law that planets travel in ellipses. According to Lowe’s account, this should be understood as a matter of the kind planet being characterized by the property travels in an ellipse. (One might query whether all laws can be given this form and so whether the fact that some general truth is a law should be explained this way. For what makes planets travel in ellipses is the fact that they have mass and hence little to do with their being planets. For example, Kepler’s law is an application of Newton’s laws, but the latter concerns quantities (mass, distance), which should be understood as universals not kinds.)” For Brian Ellis, “natural kind” may refer to natural kinds of objects (substantive kinds), natural kinds of processes or events (dynamic kinds) and natural kinds of properties and relations (property kinds).
If natural kinds exist, do they have essences? There are two ways of articulating the question of essentialism. First, one can ask whether that kind to which a particular belongs is essential to it. Thus, if a human participates in the natural kind “female,” is this biological sex category essential to her? Second, one can ask if the kinds themselves have essential properties. That is, for a woman, is there some distinct property t hat is essential for her to be a woman? Philosopher Saul Kripke has become particularly well-known for his natural kind essentialism. He argues that this essentialism is a consequence of certain semantic arguments concerning reference in support of semantic externalism. Semantic externalism is the view that the reference of a speaker’s term depends on facts external to the speaker. It is thus implicitly a form of realism.
Reconstructing the semantic arguments for externalism goes something like this: It is necessarily the case that something is a sample of water if and only if it is a sample of the water. This sample has the chemical structure H2O. Being a sample of the same substance as something entails having the same chemical structure. Therefore, it is necessarily the case that every sample of water has the chemical struecture H2O. According to some, however, P3 is non-trivial, and the reference-argument for essentalism becomes question-begging. Nevertheless, Kripke does have arguments for essentialism which are not semantic.
Gold is the element with the atomic number 79, lightning is an electrical discharge, light is a stream of photons, etc. are all examples of theoretical entities in which a common name for a kind is equated with a technical definition of it. In any case, Kripke notes that, just because something possesses the atomic number 79 does not mean that it is gold. This is a necessary condition for its being gold, says Kripke, but it is not a sufficient condition. Putnam’s famous Twin Earth experiment imagines a twin earth exactly like Earth in all respects except there is no water on Twin Earth. Instead, there is a liquid which appears and functions identically to water in every respect imaginable except in its molecular structure. Thus, there are micro-structural properties which can distinguish two entities which otherwise appear very similar on the surface. What prevents it from being water, indeed, is its micro-structural differences.
Kripke and Putnam, nevertheless, only successfully establish what may be known as a “partial essence” condition. These are conditions that are necessary but not sufficient. An essence of something, instead, refers to what is both necessary and sufficient for establishing a property as an essence of something. As Putnam and Kripke both note, water necessarily is composed of H2O molecules. Superficial similarities thus do not account for essences. Do not entities with partial essences also have full essences? Though it is necessarily the case that water is H2O, some deny that water is essentially H2O, since water is a liquid, whereas H2O can exist as a solid or a gas. Necessary qualities are not necessarily sufficient qualities.
Properties superficially associated with a kind may be neither necessary nor sufficient for kind membership. Kripke uses Kant’s example of the notion that it is a priori that gold is a yellow metal. He suggests the possibility that an optical illusion has made us falsely perceive gold as yellow when it had in fact been another color. We would intuitively conclude that we had simply been wrong rather than concluding that there is no such thing as gold. One may ask the same thing about superficially available qualities such as having two legs. Suppose it is an optical and kinaesthetic illusion that humans have two legs, when we in fact of three legs. If a descriptor of humans were “all humans have two legs,” we would simply conclude that we had been mistaken rather than concluding that there is no such thing as a human.
It is important to note that Kripke does not distinguish “necessary property” from “essential property.” The idea that something is a necessary property of something does not mean that it is an essential property of it. Kripke’s arguments for essentialism ignore this distinction, and implicitly conclude that claims about necessity are necessarily claims about essence. Kripke’s and Putnam’s arguments for essentialism do not, therefore, necessarily work. The arguments of Kripke and Putnam in favor of essentialism are basically appeals to intuition.
One of the most important issues in the philosophy of biology has to do with the nature of biological species. Species have typically been classed into species and genera in terms of their physical similarities or morphologies in Linnean biology. Nevertheless, it is only genus and taxa species which have been held to reflect fundamental, metaphysical, natural divisions. Family, order, class, phylum and kingdom, on the other hand, are merely conventions. It is only genus and taxa species which have been held to reflect natural kinds. Different biologists and philosophers of biology argue for different conceptions of species. This leads to varying extensions of different species as well as differences in numbers of species.
Kripke and Putnam both speak of animals for which they believe a posteriori essences can be found. These essences are understood as intrinsic properties which exist on a micro-structural level, and are individually necessary and jointly sufficient for an entity to be a member of this kind. Nevertheless, different biologists and philosophers of biology conceive of species differently. Ernst Mayr, for example, holds to what is known as the the biological species concept, according to which species are groups of interbreeding natural populations reproductively isolated from other populations. The phylogenetic species concept, on the other hand, holds, according to Cracraft, that a species is “the smallest diagnosable cluster of individual organisms within which there is a parental pattern of ancestry and descent.” These methods of conceiving of species and the relation of individuals to their species make extrinsic, relational properties important determinants of species membership, such as population membership and interbreeding. Thus, species essentialism may have to look beyond intrinsic properties of individuals to extrinsic properties which link different individuals together.
These issues have obvious relevance for challenges to the traditional understanding o categories such as sex or gender. What does one say about an individual presents with phenotypical female qualities, such as female genitals, but is discovered to be XY on a genetic level? Since biological sex is regarded as being at least partially, if not primarily, determined on a micro-structural level, how does one fit such an individual into the traditional male/female binary? There are different ways of dealing with such challenges to the traditional binary. Would one say that these micro-structural tendencies are the real determinants of the individual’s sex, and thus, all appearances to the contrary, one should consider the individual male instead of female? On the other hand, it would seem counterintuitive to regard an XY individual with female genitals as possessing a merely superficial similarity to other XX individuals.