Essentialism vs. Nominalism

Popper, K. (1983). Two kinds of definitions. In D. W. Miller (Ed.) A pocket Popper (pp. 87-101). Glasgow: Fontana Press

There are, apparently, two kinds of approaches to the act of defining: the essentialist approach and the nominalist approach. The former is something of a fairytale today – at least when it is spelled out up to its ultimate consequences. Popper undertakes to refute the former and support the latter.

The Aristotelian view of knowledge is singular in its emphasis on the importance, let’s say, induction. However, although bringing sense-data in the game, its overall structure was mainly Platonic. So there is opinion and there is knowledge. Opinion is opinion. But where does knowledge come from? One should say: sound arguments. Aristotle would agree, for it is the truth of the premises and the validity of the demonstration (syllogism) that makes a conclusion true. Sweet. The only thing is, this leads to an infinite regress: how do we establish the truth of the premises? By means of a valid syllogism from other premises found one-step-backwards in our reasoning. How do we establish the tr… well, you get the idea.

Against this infinite regress, Aristotle – again, one should say Plato – distinguished a certain type of intuition by means of which we come to know the truth of our most basic premises. (The ones which we should posit as a basis for our sciences, for instance. No wonder Aristotle saw his legacy as a constant search for these basic premises which would ultimately form an encyclopaedia of starting points). The statements we thus acquire are there in our head because we can grasp the essence of certain slices of reality. Long story short: science = essences + logic.

Of course, this view of definition is obsolete. The role of definitions in science is very different from what Aristotle had in mind. As a matter of fact, the whole thing works the other way around: we don’t ask “What is gravity?” and try to respond, but we ask “What is the force which draws unsuspended objects to earth?” and decide to respond “It is gravity”. To put it speech act theoretically, a definition is a kind of declarative speech act, not an assertive one. It cannot be true or false. That is why, contrary to popular belief, definitions don’t play a big role in science, but, as it were, in spreading science and understanding. They are, when all’s said & done, labels. (NB: to report of a definition is, however, subject to alethic assessment as any other assertive is).

Does this mean that such intuition do not exist? Not necessarily. We might have them on some psychological level or another. Popper’s claim is methodological: it simply means that they do not play a role in establishing the epistemological values of a claim. They are private.

But here’s another thing. Suppose we do stick to the importance of definitions. The problem with this choice, as correct as it may be, is that it is untenable. It cannot hold in principle: one cannot define all the term one uses in a theory because that would lead to an infinite regress. You define one term by other terms which, if you define, you produce more terms. This demand resembles the one that all our statements must be proved.

How can nominalism be a solution to that? Well, Popper goes, let’s first bust a myth:

Aristotelianism and related philosophies have told us for such a long time how important it is to get a precise knowledge of the meaning of our terms that we are inclined to believe it. And we continue to cling to this creed in spite of the unquestionable fact that philosophy, which for twenty centuries has worried about the meaning of its terms, is not only full of verbalism but also appallingly vague and ambiguous, while a science like physics which worries hardly at all about its terms and their meaning, but about facts instead, has achieved great precision. This, surely, should be taken as indicating that, under Aristotelian influence, the importance of the meaning of terms has been grossly exaggerated. 97

This is, more or less directly, a criticism towards Wittgenstein I, for which philosophy is primarily to concern itself with making the meaning of terms clear.