 In the second edition of Language, Truth, and Logic, Ayer attempted to remedy this problem. In a review, Church (1949a) roundly refuted Ayer’s proposal. This rebuttal sent verificationism and logical empiricism itself into a tailspin. Carnap tried to rescue these doctrines by adopting an approach not based directly on logical entailment but this effort was refuted by Kaplan (1975a). Despite these difficulties, there is currently an intense revival of interest in the question of the empirical structure and content of scientific theories and in Carnap’s work in particular (see the entry on  Rudolph Carnap).