Carnap’s Semantic Project: What Was It? And Why Did So Many People Hate It?

Logical empiricism’s leading figure, Rudolf Carnap, famously took a ‘semantic turn’ in the late 1930’s, shortly after publishing his Logical Syntax of Language. Most of the recent secondary literature on Carnap’s semantic period concerns his shift from syntax to semantics, either considered at the macro-level (e.g. Richard Creath and Thomas Ricketts), or with respect to particular topics, such as analyticity (Steve Awodey), the principle of tolerance (Alan Richardson), or truth and reference (Greg Lavers). Less attention has been paid to understanding Carnap’s semantic period for its own sake, and within its immediate historical context. This talk aims to counteract that relative neglect. I first outline Carnap’s semantic projects, as found in Foundations of Logic and Mathematics, Introduction to Semantics, Formalization of Logic, and Meaning and Necessity. This summary focuses on (i) those aspects of Carnap’s formal semantics that differ from current-day formal semantics, and (ii) the problems Carnap sets for himself, and his proposed solutions to them. The immediate reception of Carnap’s semantic work in the philosophical community is then examined. In many cases, this reception is very negative. Gilbert Ryle’s reaction is perhaps the most caustically phrased—he calls Carnap’s work “an astonishing blend of technical sophistication with philosophical naïvete” (1949, 76)—but Ryle’s basic sentiment is typical. Three of the most common objections to Carnap’s semantic works are discussed. First, semantics (at least as Carnap pursues it) is pointless or useless—for philosophy in general, and/or for the philosopher of science in particular. One form of this objection is (following Ernest Nagel): The only point of introducing semantics is to analyze, and thereby better understand, the languages we use. However, Carnapian semantic systems assume that we have a fully understood metalanguage, which must be at least as expressively rich as the object language being analyzed. Thus, Carnap’s project is otiose. Other commentators express related concerns, asserting that Carnap’s semantic theory threatens circularity (Max Black), or is merely a dictionary (C. H. Langford). Second, several of Carnap’s contemporaries object that semantic theory is illegitimate metaphysics, disguised in the “sheep’s clothing” of logical symbolism. Many commentators are especially worried that Carnap’s use of the terms ‘proposition’ and ‘property’ in his semantic definitions re-introduces a particular metaphysical stance into an enterprise that is supposedly free of metaphysics. The third objection challenges Carnap’s main positive proposal in Formalization of Logic. That book argues that the standard proof calculus should be altered, specifically by (i) adding a ‘rule of refutation’ to the usual proof calculus, and (ii) adopting a multiple-conclusion proof calculus. Carnap’s contemporary commentators object that these changes covertly smuggle semantics into proof calculi, which (all parties agree) should be purely syntactic entities. After exploring (via both published and unpublished sources) possible and actual Carnapian replies to these three objections, I briefly situate Carnap’s semantic period within the larger context of his life’s work. Specifically, Formalization of Logic continues Carnap’s earlier interest in categoricity theorems—though interestingly, Carnap himself does not explicitly draw this connection.