ESSENCES AND NATURAL KINDS Alexander Bird 1 Introduction Essentialism as applied to individuals is the claim that for at least some individuals there are properties that those individuals possess essentially. What it is to possess a property essentially is a matter of debate. To possess a property essentially is often taken to be akin to possessing a property necessarily, but stronger, although this is not a feature of Aristotle’s essentialism, according to which essential properties are those thing could not lose without ceasing to exist. Kit Fine (1994) takes essential properties to be those that an object has in virtue of its identity, while other essen- tialists refer (as Fine also does) to the nature of an object as the source of its essen- tial properties. It is sometimes important to distinguish the essential properties of a thing and the ‘full’ essence of a thing. The latter is the set of the essential properties of a thing, when that set necessarily suffices to determine the thing’s identity. One might hold that something has essential properties without agreeing that it has an identity-determining essence. Essentialism was largely in abeyance during the first two thirds of the twentieth century thanks to the domination of analytic philosophy by anti-metaphysical logi- cal empiricism and the linguistic turn. The rehabilitation of essentialism owes much to the development of a formal apparatus for the understanding of modality more generally, thanks to C. I. Lewis, Ruth Barcan Marcus, and Saul Kripke. Kripke’s dis- cussion of essentialism both about individuals and also about about natural kinds brought essentialism to wider philosophical prominence. Natural kind essential- ism, which finds its modern genesis also in the work of Hilary Putnam, claims that natural kinds have essential properties: to say that possession of property P is is part of the essence of the kind K implies that, necessarily, every member or sample of the kind K possesses P. Essentialism about individuals has been linked to thinking about natural kinds by the contentious claim that one of the essential properties of any entity is that it belongs to the natural kind (or kinds) it actually belongs to. In this chapter I shall first outline certain claims and arguments concerning es- sentialism concerning individuals (Section 2). I shall then (Section 3) introduce the notion of a natural kind in more detail before discussing natural kind essentialism (Section 4). 1 2 Essentialism concerning individuals A simple account of essentialism concerning individuals takes a’s essential proper- ties to be precisely those a possesses necessarily (reading ‘ p’ as ‘necessarily p’): (N) a possesses F essentially Fa. $ The implications in (N) may be challenged in both directions. Considering, the right-to-left implication, as Kit Fine (1994) emphasizes, it is not the case that if Fa, then a possesses F essentially. Anything is such that 2+2=4, and necessarily so, but being that way is not an essential property of every object; it is essential to the sin- gleton set containing Socrates that it contains Socrates, but while it is a necessary truth concerning Socrates that he is a member of that set, that truth is not any part of Socrates’ essence. The left-to-right implication in (N) is rarely challenged in modern metaphysics, but, it should be noted, is not required by Aristotle’s essentialism: (A) a possesses F essentially (a loses F a ceases to exist). $ ! The Aristotelian idea that a property F is essential to a when a cannot lose F without ceasing to exist is consistent with the possibility that a might never have acquired F. Some properties are persistent, in that once acquired, they are possessed at all later times, so long as the possessor continues to exist: ‘existing on 1 January 2008’ is an example, ‘being born in Boston’ (cf. Brody 1967) is another, as is ‘being a butter- fly’. The persistent properties just mentioned can be acquired but might not have been: many things existent on New Year’s Day 2008 might have ceased to exist dur- ing 2007; the mother of an unborn child might have decided to have her baby in Cambridge rather than Boston; the caterpillar may have died before metamorpho- sis (we are assuming here that metamorphosis involves a persisting individual). All persisting properties are essential according to (A), but as these examples show, they are not necessary properties of their bearers. The first two may suggest that (A) is too liberal in what it allows to be an essential property, and indeed (A) allows to be es- sential properties those which Fine rejects, since necessary properties are trivially persistent properties. Note that (A) also makes existence an essential property of any existing thing. While this may require some tightening up of the right-to-left implication of (A), for example, by reference to an entity’s nature, the Aristotelian would still claim that an entity might acquire a nature that once acquired cannot be lost. Aristotle himself thought that an embryo is not itself a human but becomes a human; but once human something cannot cease to be human without ceasing to exist. Similarly, and less contentiously, the caterpillar becomes a butterfly, but once a butterfly cannot cease to be a butterfly without ceasing to exist. As it happens, most contemporary discussions of essentialism assume (N)— which is not to say that contemporary arguments for essentialism cannot be trans- formed to support a more exacting notion of essence, such as Fine’s. Kripke argues for F’s being an essential property of a by eliciting our intuitions that a could not lack F.But since the relevant property F is in each case something that is plausibly part of a’s nature or is relevant to a’s identity, then F is at least a candidate for an essential property by Fine’s standards. 2 Kripke argues for the essentiality of (a) origin; (b) composition or substance; and (c) character or kind. We will review these arguments in turn. In responding to a passage from Timothy Sprigge (1962), Kripke raises the ques- tion, could a person, the Queen for example, have had different parents from those she actually had. Kripke is careful to distinguish (implicitly, Sprigge was not) this modal question, from an epistemic question, could we discover that the Queen’s parents are not the people we thought them to be. The answer to the latter ques- tion might, perhaps, be yes, but that does not answer the modal question: given that it is in fact true that the Queen’s parents were George VI and Elizabeth Bowes- Lyon, would it have been possible for the Queen, that very same woman, to have had different parents, say Mr and Mrs Truman (the thirty-third president of the United States, Harry S. Truman and Elizabeth Virginia Truman, née Wallace). Kripke’s an- swer is that while we can imagine that the Queen never became Queen, we cannot imagine her having different parents or being born from a different sperm and egg. Thus, more generally, a person’s origin, being born of those parents and from that sperm and egg, are necessary properties of that person. By (N), origin is essential to a person—and since origin, arguably, concerns a person’s identity or nature, ori- gin may plausibly be regarded as essential by Fine’s more exacting standards. (For a defence and elaboration of the essentiality of origin, see McGinn 1976.) Essentiality of origin is not limited to persons or even to living creatures. Kripke asks of a particular wooden table, could it have been made from a different block of wood or even from a block of ice from the river Thames. For example, the Pres- idential desk in the Oval Office is constructed from planks from the ship HMS Res- olute. Could that very same desk have been constructed from wood from different planks from different trees or even from kevlar? The kevlar desk is intrinsically differ- ent from the actual presidential desk. But the desk made from wood from different planks need not be. Could that desk have come from material of completely differ- ent origin, even if intrinsically identical to the actual desk? (Likewise Forbes points out that we can conceive of scientists constructing an zygote (fertilized egg) intrinsi- cally just like that which grew into Queen Elizabeth II. Given that she did not in fact come from such a zygote, could she have done? Essentiality of origin says no.) Kripke’s claim does not rest upon intuition alone—he does offer the following (much-discussed) supposed proof. Consider some source material suitable for a wooden desk like the presidential desk, say a certain selection of planks from the USS Rattlesnake. Could the very same presidential desk, the one now sitting in the Oval Office, have been make from the Rattlesnake planks rather than the Resolute planks? Here is an argument as to why not. Consider a world like ours except that in addition to the making of the presidential desk (call it ‘P-desk’) another, intrinsi- cally identical desk is made from the Rattlesnake planks (call this ‘Q-desk’). Clearly P-desk and Q-desk are different desks. Now consider a third world, in which no desk is made from the Resolute planks but a desk is made from the Rattlesnake planks. That would be Q-desk, and since Q-desk , not P-desk, the desk made from the Rat- tlesnake planks is not P-desk. So P-desk, the actual presidential desk, could not have been made from the Rattlesnake planks, nor, for the same reasons, from any other hunk of matter that is entirely distinct from the matter from which it was actually made.