This book was born from the desire to conduct an inquiry into the heterogeneity and variety of linguistic theories in order to assess their descriptive and explanatory power. The first part of the volume brings together contributions addressing formal and theoretical issues. It focuses on the specific questions of metalinguistic discourses, representations and formal symbols, and considers the case of representations pertaining to different metalinguistic levels and their possible translation from one level to another. The essays compiled in this section also examine how generative semantics paved the way for current trends in cognitive linguistics, and provide an analysis of the historical and epistemological context of the notion of metafunction found in Systemic Functional Grammar. The contributions gathered in the second part of the book evaluate the results of a certain number of linguistic studies, putting various theories to the test. They specifically discuss the notion of intersective gradience, analyse modality and the question of irony within two different theoretical frameworks, and deal with parenthetical verbs in the light of an utterer-centred approach.This book will appeal to all linguists with an interest in linguistic theories, to advanced students in linguistics, as well as to scholars in cognate fields such as epistemology, philosophy of language, psychology and neurosciences.