Boskovic treated unobservables in two different ways. During his earlier period (1741-48) the difference between observables and unobservables was a significant element of his specific semantic instrumentalism. The sentences of unobservables (such as absolute space, time and motions) were treated only as convenient tools conceived to provide for the empirical success of a theory. Later, especially in his Theory of Natural Philosophy (1763), Boskovic relativized this distinction by positing absolute properties (continuity and impenetrability), which are common to both observables and (...) unobservables. As a scientific realist he was committed to his original unobservable entities, i.e. “points of matter”. Due to the intrinsic paradox contained in the concept of these points, his realist position was led to the absurd, which demands an anti-realist interpretation of Boskovic's theory. (shrink)