In this book, Brice Halimi revives the connection between philosophy of language and philosophy of mathematics which founded analytic philosophy. Russell's logical analysis in The Principles of Mathematics aimed to identify the 'logical constants' of language with the 'indefinables' of mathematics. However context-sensitivity, which covers all the cases in natural language where the semantic content of an expression depends on the context of its utterance, is thought to hinder that program. In contrast, Halimi argues that context-sensitivity, approached as a radically dynamic process based on context-shift, is amenable to a mathematical counterpart, but that new mathematical concepts are needed. His approach leads to a renewed conception of semantic content, linguistic meaning, and their interaction, while also reconsidering the divide between semantics and pragmatics. The book will interest philosophers of language and philosophers of mathematics, and also has numerous applications to philosophy of mind, epistemology, logic, and linguistics.