How to talk about unobservables
Frederik Müller, Bas C. van Fraassen · Analysis · 2008
In this journal, Dicken & Lipton (2006) argued, notably following Musgrave (1985), that a constructive empiricist cannot coherently draw the distinction between observable objects (events, processes, ...) and unobservable ones. We argue to the contrary: the distinction can be drawn coherently. Furthermore, we point to a flaw in these and similar criticisms: they proceed from the syntactic view of scientific theories whereas constructive empiricism is and has always been wedded to the semantic view, a fact that has consequences for the characterization of empirical adequacy and hence for the formulation that constructive empiricism favours. It was emphasized from the beginning that to say that a theory is empirically adequate just if all it says about observable things is true, is only a rough, informal way (van Fraassen 1980: 12). Rough and informal, but also immediately marked there as inadequate: it presents the notion of empirical adequacy for the conception of a theory as a set of sentences in a well delineated language. The main reason for rejecting that conception was precisely that it cannot give us an adequate notion of empirical adequacy: every way to do it seems to rely on the troublesome distinction between ‘theoretical’ and ‘observational’ predicates in the language of the theory. Further, you certainly cannot tell whether a sentence is about, or is only about, observable objects by looking at its syntactic form, or at the predicates in it: The empirical import of a theory cannot be isolated in this syntactical fashion, by drawing a distinction among theorems in terms of vocabulary. If that could be done, T/E would say exactly what T says about what is observable and what it is like, and nothing more.1 But any unobservable entity will differ from the observable ones in the way it systematically lacks observable characteristics. As long as we do not abjure negation, therefore, we shall be able to state in the observational vocabulary (however conceived) that there are unobservable entities, and, to some extent, what they are like. ... Thus on the syntactic approach, the distinction between truth and empirical adequacy reduces to triviality or absurdity, it is hard to say which. (van Fraassen 1980: 54–55)