In this paper I will be reviewing literature, mostly from cognitive science, related to the human brain’s processes of categorization

C.Essences and reproduction

Rips (1989) gave adults a story about an animal he called a ‘sorp’, and which was described as having feathers, flying, making nests, etc.all of the characteristics of a typical bird. This sorp came into contact with some toxic waste and underwent some transformations: shed feathers, developed transparent, membranous wings, a brittle, iridescent, outer shell, etc.all of the characteristics of a typical flying insect. The transformed sorp eventually met a normal female sorp and mated, which led to the laying of eggs which in turn produced normal sorps. He calls this the ‘accident’ manipulation.

In a 1 to 10 scale where 1 is ‘insect’ and 10 is ‘bird’, subjects’ mean ratings were as follows: in the categorization condition, they rated the animal a 6.5 (i.e. most thought the transformed sorp was more likely to be a bird than an insect); in the typicality condition, a 4 (i.e. most thought the transformed sorp was more typical of an insect than a bird); and in the similarity condition, a 3.5 (ditto).

This shows two things. (1) The independence of similarity and categorization; and (2) The importance of what I believe is the necessary and sufficient condition for categorization in a natural living kind: biological descent. Notice: the transformed sorp is nevertheless the offspring of normal sorps, and produces normal sorps in reproduction, therefore, despite appearances, it is still a bird and not an insect. What I would like to see now is a modification of Rips’ experiment such that the transformed bird, in addition to all its other changes, lays eggs asexually and these, when hatched, resemble the transformed parent. I predict that respondents would say the transformed sorp is now an insect.

Although I think biological descent is necessary and sufficient for membership in a biological kind, I do not think this is tantamount to saying that biological descent from a given biological kind equals the kind’s ‘essence’. It seems to me that an ‘essence’ can only be made up of predicates constituting one or more properties, else we are no longer speaking English.

By this real essence I mean that real constitution of anything, which is the foundation of all those properties that are combined in, and are constantly found to co-exist with, the nominal essence: that particular constitution which everything has within itself, without any relation to anything without it.—Locke (1964; quoted in Keil 1989)

Certainly, one might say that ‘ability to reproduce the kind’ is perceived as part of a biological kind’s essence (and I would hazard that it is), but this is obviously different from saying that the essence consists in being descended from members of the kind, for this is not really a property but a statement of history. Thus, I believe biological descent from a given biological kind is taken as the necessary and sufficient condition for the possession (through inheritance) of that kind’s essence, and that one of the predicates assumed of any biological kind essence will be ‘ability to reproduce the kind’.

In a normal world, I submit, one has a given, biological-kind essence if, and only if, one is biologically descended from members of that kind. However, it is possible that in a fanciful world of weird toxic wastes, acquiring the essence some other way is an idea that can be entertained. This is why doing the above-mentioned modification to Rips’ experiment would be so relevant for my hypothesis: if people call the transformed sorp ‘an insect’ when it generates insect offspring in reproduction, but not when it produces normal sorps, this suggests that ‘ability to reproduce the kind’ is part of the essence, and that reproduction transfers the essence.

D.Essences and Insides

Gelman & Wellman (1991) carefully distinguish between insides and essences as follows:

The insides of an item are the matter residing physically behind or under its outer layer (e.g., the bones, heart, and blood of a dog , the stuffing and wires of a chair). Insides are concrete and ultimately observable, yet typically remain unobserved. An essence is the unique, typically hidden property of an object that makes it what it is, without which it would have a different identity (e.g., the chemical composition of water, the DNA structure of an elephant). Essences generally are never observed, and in fact may remain unknown (consider, for example, the essence of life, or the essential nature of humans).

Both insides and essences are difficult to define precisely. Do a dog's insides begin under the fur, under the skin, under the flesh, or indeed even interior to the skeletal framework? More troubling still, essences are typically unknown; those insensible parts or cores that enable or cause the sensible qualities of an object. Essences are often unspecifiable, and by their nature require an inference about some deeper organization or disposition.
The distinction is salutary because humans probably do not equate the insides with the essence as if they were coextensive. However, it seems very likely that we think of essences as somehow located ‘inside’. Whatever it is that makes a thing the thing that it is—its essence—we do not imagine it as lying on the surface of the thing, but somehow inside it, even if we may deny that the essence amounts to nothing more and nothing less than the thing’s insides.

Young children understand very little about how the insides of a natural living kind are related to its function. And yet, it was found that with natural living kinds (e.g. rabbit) but not with other kinds of things (e.g. box) children tended to reason that the function changed when the insides rather than the outsides were removed (Gelman & Wellman 1991). This is consistent with the idea that they believe the essence is inside and that removing the insides will take the essence with them, thus altering the nature of the thing. If children assume the essence is inside and is responsible for the thing having a particular nature, then they will be found to reason as in Gellman & Wellman (1991) even if their knowledge of the actual insides and their relationship to function is extremely poor.