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 differences are not the essential differences themselves, but are, so to speak, signs of them, symptoms, clues, superficial manifestations of the being of something else that we cannot know. We infer the presence of essential differences through a semiotic process, with knowable accidents as our point of departure.11
That the effect is a sign of the cause is Thomas’s customary idea (much of his theory of analogy depends on this assumption, which is, if we were to trace it back, Stoic in origin: effects are indicative signs). The idea reappears, for instance, in Summa Theologiae I, 29, 2 ad 3 and I, 77, 1 ad 7: a difference such as rational is not the real specific difference that constitutes the substantial form. Ratio (reason) as potentia animae (a power of the soul) appears outwardly verbo et facto (in word and deed), through exterior actions, psychological and physical behaviors (and those actions are accidents, not substances!). We say humans are rational because they demonstrate their rational powers by means of acts of cognition, or by an internal discourse (the activity of thought) or an external discourse, that is, by means of language (Summa Theologiae I, 78, 8 co.). In a decisive text in the Contra Gentiles (3, 46, n. 11), Thomas says that human beings do not know what they are (quid est), but they know what they are like (quod est) insofar as they perceive themselves as actors in rational thought. We know what are our spiritual powers only “ex ipsorum actuum qualitate” (“from the nature of these same acts”). Thus rational is an accident, and so are all the differences into which the Porphyrian tree can be dissolved.
From this discovery, Thomas does not draw all the conclusions he should have regarding the possible nature of the tree of substances: he cannot bring himself (psychologically perhaps) to call the tree into question as a logical tool for obtaining definitions (something he could have done without going out on a limb), because the entire Middle Ages is dominated by the conviction (however unconscious) that the tree mimics the structure of reality, and this Neo-Platonic conviction also affects the most rigorous of Aristotelians.
It is clear, however, if we follow its inner logic, that the tree of genera and species, however constructed, explodes into a swirl of accidents, into a nonhierarchizable network of qualia. The dictionary dissolves of necessity, as a result of internal tensions, into a potentially orderless and limitless galaxy of elements of knowledge of the world. It becomes, in other words, an encyclopedia, and it does so because it was already in fact an encyclopedia without knowing it, an artifice invented to camouflage the inevitability of the encyclopedia.
1.2.2. The Utopia of the Dictionary in Modern Semantics
We see a return to the dictionary model in the linguistics of the second half of twentieth century, when the first attempts appear to postulate or recognize—in order to define the contents expressed by the terms of a natural language—a finite system of figures possessing the same characteristics as a phonological system (based on a limited number of phonemes and their systematic oppositions). Thus, a feature semantics (features being primitive semantic atoms) was postulated, designed to establish the conditions necessary and sufficient for a definition of meaning, excluding knowledge of the world. In this way, in order to be recognized as a cat, something must have an ANIMAL feature, but it is not requested that it meows. These necessary and sufficient features are dictionary markers. Something along these lines was anticipated by Hjelmslev (1943[1961]) when he proposed to analyze the concepts corresponding to the twelve terms ram, ewe, boy, girl, stallion, mare through a combination of the male/female opposition and the assumed primitives SHEEP, HUMAN BEING, CHILD, HORSE.
Hjelmslev’s was not the only modern proposal for a dictionary representation, though the many others proposed in the area of linguistics or of analytic philosophy, almost always in ignorance of Hjelmslev’s proposal, did no more than repropose his model.12
Reconsidering Hjelmslev’s model, we see that a dictionary representation would allow us to solve the following problems (as Katz 1972 will suggest later): synonymy and paraphrase (a ewe is a female ovine); similarity and difference (the pairs ewe and mare and mare and stallion have some features in common, while we can establish on the basis of what other features they can be distinguished); antonymy, complementarity, and contrariety (stallion is the antonym of mare); hyponymia and hyperonymia (equine is the hyperonym of which stallion is the hyponym); sensibleness and semantic anomaly (stallions are male makes sense while a female stallion is semantically anomalous; redundancy (male stallion); ambiguity (the terms bear and bull, for example, have more than one meaning); analytical truth (stallions are male is analytically true, because the definition of the subject contains the predicate); contradictoriness (there are no male mares); syntheticity (that ewes produce wool does not depend on the dictionary but on our knowledge of the world); inconsistency (this is a ewe and this is a ram cannot be equally true if referred to the same individual); semantic entailment (if ram, then ovine).
Unfortunately this model does not permit us to represent what we must know about sheep and horses if we are to understand many discourses about them. It does not allow us, for instance, to reject expressions like the stallion was bleating desperately like a ram (justifiable only in a metaphorical context, and a very daring one at that), given that the mechanism of definition does not explain what sound horses naturally emit.
And this is not all. Even if a system of this kind could be implemented based on assumed primitives, and if SHEEP and HORSE were primitives, they would serve to define only a very limited share of the terms concerning part of the animal kingdom. How many primitive features would be needed to define all the terms in any given lexicon? And how do we define a “primitive” feature?