Distinctions between whales and fish are more influenced by cultural and linguistic changes than by scientific discoveries.

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“The whale, the limpet, the tortoise, and the oyster. . . as men have been willing to give them the name of fishes, it is wisest for us to conform.”

—Oliver Goldsmith (1728-1774; quoted in the Oxford English Dictionary)

In a paper some years ago I claimed that, contrary to a widely held misapprehension, whales were perfectly respectable fish. I must confess, however, that I have since come to doubt this claim about whales. The reason for this, though, is not that I have come to see that the march of science was indeed irresistible. It is rather that I have come to doubt whether there is any sense in which such a well-entrenched tenet of folk biology as that which excludes whales from the ranks of fish could be shown to be wrong. Thus I still think that folk once believed that whales were fish, and that they were duped into changing that belief for bad reasons. Before this unfortunate occurrence, whales indeed were fish. But I take it that now almost all educated people are quite confident that whales aren’t fish. And this, I now think, is enough to show that they are right that whales are now no longer fish.

Let me begin by considering briefly what is a whale and what is a fish. We may, I think, be quite confident that these are terms of ordinary language. My four-year-old son is a quite competent user of both, and I take it that he is not especially precocious in this regard. To begin with whales, I suppose that many, in the scientistic spirit theorized by the philosopher Hilary Putnam, would now try to identify whales with the order Cetacea. In support of my strong intuition that dolphins and porpoises are not whales, however, I am pleased to note that Webster’s defines whale as “any of the larger marine mammals of the order Cetacea, esp. as distinguished from the smaller dolphins….” Dolphins and porpoises do not form any significant subgroup of the order Cetacea. This order is, indeed, commonly divided into two suborders, namely the Toothed whales and the Baleen whales. Although dolphins and porpoises may constitute a specific lineage of the Toothed whales, proposing a dichotomy between this lineage, on the one hand, and all other lineages of toothed whales plus all the Baleen whales, on the other, makes no biological sense. Note also that dolphins are more closely related phylogenetically to Toothed whales than these latter are to Baleen whales. In sum, then, the category of whales is a biologically arbitrary one. In agreement with Webster’s we may plausibly conclude that the reason dolphins and porpoises are not whales is much more prosaic: They aren’t big enough. Very large size is central to the ordinary language concept of a whale. In fact the word “whale” is often used as a metaphor for largeness or excess as, for instance, in “a whale of a time.”

The whale and the sturgeon were once known as the royal fish. The great fish that swallowed Jonah is also referred to as a whale.

Similar remarks apply to the concept of fish. As the quotation by Oliver Goldsmith at the beginning of this essay suggests, the term is sometimes used very widely for any aquatic animal. This usage is suggested by the various aquatic animals, such as starfish, cuttlefish, crayfish, and generically, shellfish, whose names contain the suffix fish but which most people would decisively exclude from the extension of that term. The Oxford English Dictionary in fact does offer the definition as “any animal living exclusively in the water” for popular language but adds a “scientific” usage which restricts the term to cold-blooded vertebrates with gills. Webster’s begins with a version of this scientific definition and adds “(loosely) any of a variety of aquatic animals.” This scientific definition applies to members of the classes Chondrichthyes (cartilaginous fishes), Osteichthyes (bony fishes), and Agnatha (jawless fishes). But there is little or no biological rationale for a category containing just these groups. The primitive and rather unpleasant species in the class Agnatha (lampreys, hagfishes, and slime eels) have little in common with a state-of-the-art carp or tuna. Sometimes, it is true, the agnaths are distinguished from the other two classes, only the later being denominated “true fish.” But in fact a shark and a salmon are barely more closely related to one another than either is to a lamprey.

Thus the notion that there is a “scientific” usage of the word “fish” is a decidedly suspect one. The appeal in the definition to such technical matters as the possession of gills or cold-bloodedness seems rather a quasi-scientific rationalization of an extra-scientific linguistic intuition than the report of a genuinely scientific usage. Indeed, as is so commonly the case with attempts to define biological kinds, it is not even strictly true of all its intended referents. Some species of tuna maintain body temperatures as much as 20 degrees higher than their surroundings, and so should qualify as warm-blooded. And the lungfish Protopterus has been shown to get only 10 percent of its oxygen from water through its reduced gills. If its gills were to disappear completely at a subsequent evolutionary stage, I doubt whether it would thereby cease to be a fish. Given, then, that neither “whale” nor “fish” is really a scientific term, the rationale for the dictum taught religiously to all our children that whales are not fish (and it is interesting that it is something that reliably requires to be taught) is more than a little unclear.

I have not attempted to do a historical study of this usage, but it is clear that whales have not always been nonfish. The whale and the sturgeon were once known as the royal fish. The great fish that swallowed Jonah is also referred to as a whale. And so on. Moreover there are obvious reasons for including whales in the (nonscientific) category of fish. A dolphin is in many ways a similar beast to a tuna. Both are superbly adapted to swimming at high speeds, and consequently they show considerable analogous evolution in superficial morphology. Certainly they are a lot more superficially similar than either is to an eel, a sea horse, or a ratfish, or, for that matter, to a bat, a rabbit, or a sloth. Given, then, that whales were once seen as fish, and that neither “whale” nor “fish” is in any serious sense a scientific taxonomic term, it is interesting to speculate, at least, as to how they became nonfish.

Why Whales Are Not Fish

Despite the foregoing considerations, I have already conceded the obvious fact that whales are not fish. Why not? We might ask both why this fact is obvious, and why it came to be a fact at all. The first question is easy enough. Educated speakers will, I suspect, almost unanimously refuse to apply the word “fish” to, Blue whales, Killer whales, and similar creatures and, for that matter, to dolphins. Ultimately I suppose that this is the only relevant evidence, and that it is decisive. On the other hand, I also suspect that if pushed to rationalize this linguistic intuition, most people will be found to believe that scientists have found out what fish are, and what whales are, and that the latter are distinct from the former. Here, as I have argued, they would be mistaken. What a fish is is not the sort of thing a scientist (except, perhaps, a linguist) could find out.

Much more interesting, then, is the second question. Is there a good reason for teaching our children that whales are not fish? Even if these are not scientific categories, one might argue that some useful scientific knowledge is transmitted by using them this way. Whales are, after all, mammals, and no other mammals are much like fish. Being mammals ourselves, we tend to know quite a bit about this class of organisms, and we certainly learn a good deal about whales by knowing that they are mammals. But this argument is not compelling. The obvious rejoinder is that some mammals are fish. In fact, if we taught our children that whales were mammalian fish, they would both learn to apply general knowledge about mammals to whales (they bear live young and suckle them, are warm-blooded, etc.) and might also learn that “fish,” unlike “mammal,” was not a term for any coherent scientific grouping of organisms but a loose everyday term for (perhaps) any aquatic vertebrate. Indeed, the argument that because whales are mammals they cannot be fish seems to me to be a paradigm for the confusion between scientific and ordinary language biological kinds. (I shall return to this point in the next section.)

In some ways a more satisfactory answer to the present question might be a moral one. Certainly our sense of appropriate treatment of cetaceans is greatly influenced by the conviction that whales are not fish. Nowadays, if one offers someone the choice between a tuna sandwich or a whale steak, one will notice a strong tendency to choose the former and even some degree of outrage at being offered the latter. Even some people with moral objections to eating any mammals will sometimes consider it acceptable to eat fish. This perhaps points toward the greatest respect in which whales really do diverge from typical stereotypes of fish. We think of fish as being fairly stupid creatures and of whales, even by mammalian standards, as being decidedly bright. Although no doubt the emphasis on intelligence in deciding how bad it is to kill and eat something has an anthropocentric aspect — intelligence being of course what we take to be so special about ourselves — there is surely something plausible to the idea. Killing a highly intelligent animal will perhaps cause great grief to its relatives and school-friends, and perhaps even will put an end to a more intrinsically valuable life. But certainly this point has at most rhetorical force. There is no reason why some kinds of fish should not be much more intelligent than others. Certainly there are such differences among mammals (between a human or whale, say, and a shrew) and perhaps there are comparable distinctions in intelligence between different kinds of non-cetacean fish. Moreover I take it that whales ceased to be fish long before anyone was much troubled by eating them — indeed in many countries it appears that they are still not much troubled by doing so. So certainly this is not the historical explanation for the change.

For want of a better explanation, I conclude that the exclusion of whales from the category of fish developed as a response to greater scientific knowledge of the nature of whales, which was, as I have argued, a somewhat misguided response. No doubt such infiltrations of ordinary language by science are common enough. So I now turn to a more general consideration of the relation between scientific and ordinary language terms for biological kinds.

Science and Ordinary Language

The general point of the discussion so far is to insist that ordinary language and science provide largely independent and often disjoint ways of classifying the biological world. Where ordinary language biological kinds are distinct in extension from any coherent scientific kind, the attempt to revise them in accord with supposedly scientific discoveries can promote only confusion. Moreover, as I have argued elsewhere. I take it that ordinary language classifications are typically quite as well-motivated, and the kinds to which they refer may be just as objectively real, as biological classifications. It is just that they are differently motivated.

Thus onions may constitute a perfectly real class of organisms, but not one that biologists have found any good reason to classify together. There are presumably objective facts about organisms of certain species that make them suitable for flavoring stews though I must admit that I cannot confidently vouch for the fact that all the species referred to as onions meet this condition. Similarly with fish, though the rationale for this much broader category is perhaps a lot vaguer. On the other hand, it is clear that to call these systems of classification wholly independent would be an exaggeration. For better or worse, the development of scientific thinking sometimes has an impact on ordinary language usage.

One important aspect of this interaction is the importation of relatively pure scientific categories from scientific taxonomy into ordinary language. I have already suggested that this is the way that many species terms should be understood. Here the amateur naturalists who are the primary users of such terms have an explicit interest in distinguishing those species recognized by professional biologists, and ordinary language terms are treated as synonyms for Latin binomials. Perhaps of greater interest are the constructions of ordinary language terms to acknowledge higher-level taxonomic distinctions developed by biologists. Several examples have occurred in the foregoing discussion.

It is, I think, not widely accepted that there are any matters of much importance about which science has nothing to say.

One of the most familiar examples is “mammal.” This, surely, is a term imported into common usage from scientific taxonomy. Less familiar, but similar, examples are the jawless fish, cartilaginous fish, and bony fish also mentioned. The point of these terms is to be able to make biologically significant distinctions in somewhat more user-friendly ways than by learning terms such as Osteichthyes or Chondricthyes. Whereas the latter serve purposes such as international standardization important for biologists, the former are both easier to remember and more informative for less technical scientific or quasi-scientific discourse. I take it, however, that “is a member of the class Agnatha” and “is a jawless fish” are perfect synonyms, with scientific practice determining the reference. (Being a jawless fish does not mean being a fish and being jawless, or it would apply to all those bony fishes on the fishmonger’s slab that have had their heads cut off.)

I want to claim, however, that these imported terms from scientific discourse should be understood quite differently from more familiar and well-entrenched ordinary language terms, and that the failure to make this distinction indicates a significant confusion common to many philosophers and lexicographers. Whereas the definition of mammal as, say, “warm-blooded, hairy vertebrate with a four-chambered heart and which nourishes its young with milk from maternal mammary glands” is entirely appropriate, the definition of fish as “cold-blooded, aquatic vertebrate with gills, and (usually) scales, fins, etc.” is much more questionable. These definitions look very much alike. But, I have suggested, the terms to which they apply are of quite different kinds. Thus, while it is quite appropriate to say that it is a scientifically attested fact that all mammals have four-chambered hearts, it seems to me something like a category mistake to say that it is a scientific fact that all fish have gills — not because they might not but because science has nothing to say about all fish. This last remark perhaps gets to the heart of the present problem. It is, I think, not widely accepted that there are any matters of much importance about which science has nothing to say.

And certainly the question, What kind does this organism belong to? will strike most people as paradigmatically the kind of question about which science must be the only authoritative arbiter. Ironically, perhaps, the idea of an authoritative and unique answer to such a question really assumes some version of essentialism, the idea that some fundamental, essential property of a thing makes it the kind of thing it is, and essentialism was central to the Aristotelian and Scholastic views of knowledge against which modern science developed in large part as a critical reaction. Essentialism in biology, more specifically, was delivered its death blow by the triumph of Darwinism, and the consequent recognition that an organism might belong to a quite different kind from its ancestors, and that variation rather than uniformity was the norm for a biological kind. In a biology premised on variation and change, there is no reason to expect any unique answer to questions about how organisms should be grouped together, and a fortiori, there is no reason to expect science to provide such answers.

I do not want to deny the possibility that there might be scientifically motivated revisions of ordinary language biological kinds for which the revision might be sufficiently justified by some biological knowledge that it would somehow convey, though I am not convinced that there are such. Certainly there are many cases in which we change our views as to what higher level, scientifically defined, kinds familiar ordinary language kinds belong. But as in the case of whales and fish, whereas it is certainly of interest to recognize that whales are mammals, this fact has no bearing that I can see on whether they are fish. The majority of cases that come to mind are of just this kind. So, for instance, it is sometimes said that marsupial mice are not really mice. The point, of course, is that Australian mice are very distantly related to mice in most of the rest of the world. For the slightly more technical this reflects the divide between marsupial and placental mammals, and I take it that these kinds, unlike mice, certainly, are pure scientific imports. (Indeed I take it that while the notion of a marsupial is a fairly familiar one, many fewer people can correctly contrast it with a placental.) Since “mouse,” on the contrary, is an ancient and well-entrenched term of ordinary language, the denial that marsupial mice are real mice is again based on an illegitimate interplay between categories of quite different kinds.

It may be that excessive scientism, whether among lexicographers, high school science teachers, or just regular folk, will continue to favor a continuing convergence between scientific and ordinary language taxonomies. If this is the case, it does not reflect a gradual Piercean convergence on some objective reality but, rather, the hegemonic power of one, sometimes imperialistic, method of knowledge production. Perhaps for most folk in the West such imperialism is relatively harmless; for most of us urban and suburban folk what we call organisms doesn’t matter very much. And even for folk more intimately connected with nature, I do not suppose that adopting Western scientific modes of classification would bevery damaging to their dealings with natural objects. Probably in those cases in which they would be damaging, folk will refuse to adopt them.

Nevertheless, there are reasons for resisting, or at least pointing out, this imperialism. With regard to its effects on Western culture, the main such reason is simply to resist the excesses of scientism. The achievements and successes of science are amply evident, but it is also important that human culture has aims and projects that are distinct from and incommensurable with those of science, and science does not hold the answer to every question of human interest. Quasi-scientific doctrines such as that whales have been discovered not to be fish help to obscure this point. With regard to our view of non-Western biological classification, this moral may be more important. Especially in relation to cultures with more regular and direct interaction with nature, we would do well to explore thoroughly the basis and function of such classifications before criticizing them for their nonconvergence on our own scientific categories. Once again, the perception of the value of Western science will hardly be enhanced by insisting on unsubstantiated claims to insight where this is not to be had.

John Dupré is Professor of Philosophy of Science at the University of Exeter and Consulting Director of Egenis, the Centre for the Study of Life Sciences. He is the author of several books, including “Darwin’s Legacy” (Oxford University Press) and “The Metaphysics of Biology” (Cambridge University Press). This article is excerpted from a longer essay first published in the volume “Folkbiology.”

Author’s note: Since originally writing the chapter from which this excerpt is drawn, I encountered Graham D. Burnett’s book, “Trying Leviathan: The Nineteenth-Century New York Court Case That Put the Whale on Trial and Challenged the Order of Nature” (Princeton University Press, 2010). Burnett explains how the categorization of whales as fish was the focus of a prolonged, fascinating and then notorious legal battle over whether whale oil was subject to a tax on fish oil. As so often, real life is even more interesting than theory.