 The logical positivists explored the idea that the meaning of a sentence is a procedure for determining the truth or falsity of that sentence. From this perspective, studies of linguistic meaning and propositional structure still dovetail, even if natural language employs “conventions” that make it possible to indicate complex propositions with grammatically simple sentences; see the entry on  analysis.  But to cut short a long and interesting story, there was little success in formulating “semantic rules” that were plausible both as (i) descriptions of how ordinary speakers understand sentences of natural language, and (ii) analyses that revealed logical structure of the sort envisioned. (And until Montague [1970], discussed briefly in the next section, there was no real progress in showing how to systematically associate quantificational constructions of natural language with Fregean logical forms.)