According to Richard Gaskin, The Problem of the Unity of the Proposition is to explain 'what distinguishes propositions from mere aggregates, and enables them to be true or false' (18).1 This problem arises from the simpler problem of distinguishing a sentence from a 'mere list' of words (1). The unity of a sentence is due to its syntax, a level of structure which is not apparent in the string of words which are uttered or written, and which distinguishes a sentence from a list. However, if one holds that sentences express propositions that are composed of objects which serve as semantic referents of its words, then the problem of unity becomes one about the metaphysics of propositions. What constitutes a proposition and distinguishes it from a mere aggregate of its constituents? If it is some relation between the constituents, and that relation is a constituent of the proposition, needing another relation to relate it to the others, then we seem to fall into a familiar difficulty, 'Bradley's Regress.' For Gaskin, however, rather than being a problem for explaining unity, Bradley's Regress is the solution to our problem; it explains 'the unity of the proposition.' F.H. Bradley's regress was originally formulated by Bradley as an argument against the reality of relations. It was a problem for explaining the relation of exemplification which holds between objects and universals, including relations, [End Page 469] that are in the world. There is indeed a problem of unity raised by this 'exemplification regress,' one might think, but it is a problem about the unity of facts, or things in the world that make propositions true, rather than a problem for propositions, which are truth bearers or made true or false by things in the world. In response to those who might think that the relation of exemplification is at best a constituent of facts in the world rather than propositions that are true of the world, Gaskin offers his thesis of Linguistic Idealism, which holds that facts (and so the world) are propositional in nature.2 It then turns out that Bradley's Regress, which is about the nature of exemplification, in fact concerns the unity of propositions. The grand conclusion of Gaskin's elaborate argument, thus, is that the regress is not vicious, as many have held, but in fact an '...innocent, constituting regress' (xi). Gaskin's thesis of 'linguistic idealism' just serves along the way, although almost as a subtext, or conclusion, as important as the official problem of the unity of the proposition. Here Gaskin is even more confident than with his notion of the regress. He attacks the more common view of a distinction between propositions and their truth makers in the world: 'The whole idea of a non-propositional underlying reality is fantastical' (124).
That's the short version for someone who wants to know where the discussion is going before working through Gaskin's lively and well written 450-odd-page book with more than 1,500 footnotes and 750 items in the bibliography. Even readers who aren't convinced of his ultimate conclusions will certainly benefit from detailed discussions of a wide range of issues in recent philosophical semantics that come out of the book. This is an immense work of scholarship. Gaskin has read and studied all of those items in the bibliography, and uses them at every step to bolster his argument. The book will be of lasting value for that survey of literature alone.
After a brief survey of antecedents going back to Plato's Sophist, Gaskin works forward, to the classic statement of 'The Problem of the Unity of the Proposition in Bertrand Russell's Principles of Mathematics,' and then devotes most energy to the philosophy of Frege and its recent interpreters following Michael Dummett. The problem of the unity of the proposition in its modern form comes from Russell: [End Page 470]
Consider, for example, the proposition 'A differs from B.' The constituents of this proposition...