From the Tree to the Labyrinth Read Free Page B

CANINES, of the suborder of FISSIPEDS, of the order of CARNIVORES, of the subclass of PLACENTALS, of the class of MAMMALS. This classification, however, does not tell us (and is not meant to tell us) either what the properties of a dog are or how to recognize a dog or refer to a dog. Every node of the classification is in fact a pointer that refers to another chapter of zoology in which the properties of Mammals, Placentalia, Carnivores, Fissipeds, and so on are specified.
    A dictionary classification, then, does not serve to define a term but merely to allow us to use it in a logically correct fashion. Given, let’s say, that the imaginary order of the Prixides is classified as belonging to the genus Prosides and the Prosides are a species of the genus Proceides, we do not need to know what the properties of a proceid or a prosid are to draw (true) inferences along the lines of: if this is a prixid then it has to be a prosid, and it is impossible that something that is a prixid should not be a proceid.
    But these are not the bases which allow us to understand expressions in which terms like prixid and proceid appear: it is one thing to know that it is logically incorrect to say that a prixid is not a proceid; it is quite another to say what a proceid is, and, if it means anything to say that terms have a meaning, the classification does not supply that meaning.
    Gil (1981: 1027) suggests that genera and species may be used as extensional parameters (classes), whereas only the differences decide the intensional regime. This is tantamount to saying that the meaning of a term depends on the differences and not on the genera or the species. Now, what makes it difficult to regiment the differences under a Porphyrian tree is that the differences are accidents, and accidents are infinite or at least indefinite in number.
    The differences are qualities (and it is no accident that, while genera and species, which represent substances, are expressed by common nouns, the differences are expressed by adjectives). The differences come from a tree that is not the same as the substances, and their number is not known a priori ( Metaphysics VIII, 1042a–1042b). Granted, Aristotle makes these remarks about nonessential differences, but at this point who can say which differences are essential and which not? Aristotle plays on a few examples (like rational and mortal ), but when he speaks about species other than human, such as animals or artificial objects, he becomes much more vague and the differences multiply.
    In theory we are entitled to put forward the hypothesis that Aristotle would not have been capable of constructing a finite Porphyrian tree, but in practice as well (on the basis, that is, of the philological evidence), when we read On the Parts of Animals, we see that he gives up in practice on constructing a single tree and readjusts complementary trees according to the properties whose cause and essential nature he wishes to explain (cf. Balme 1961 and Eco 1983a).
    The notion of specific difference is, rhetorically speaking, an oxymoron. Saying specific difference is tantamount to saying essential accident. But this oxymoron conceals (or reveals) a far more serious ontological contradiction.
    The thinker who understood the problem without prevarication (though he pointed it out with his customary prudence) was Thomas Aquinas. In his De ente et essentia he says that specific difference corresponds to substantial form (another ontological oxymoron, if we may put it that way, since the most substantial thing we can think of is identified with an accident). But Thomas’s thought does not leave room for misunderstanding: what defines substantial form is difference as an accident.
    In order to justify such a scandalous conclusion, Thomas excogitates—with one of his habitual strokes of genius—an extremely brilliant solution. There exist essential differences; but which and what they are we do not know; what we know as specific