The topic of this book is the theoretical foundations of a theory LSLT -- Lexical Semantic Language Theory - and its implementation in a the system for text analysis and understanding called GETARUN, developed at the University of Venice, Laboratory of Computational Linguistics, Department of Language Sciences. LSLT encompasses a psycholinguistic theory of the way the language faculty works, a grammatical theory of the way in which sentences are analysed and generated -- for this we will be using Lexical-Functional Grammar -- a semantic theory of the way in which meaning is encoded and expressed in utterances -- for this we will be using Situation Semantics -, and a parsing theory of the way in which components of the theory interact in a common architecture to produce the needed language representation to be eventually spoken aloud or interpreted by the phonetic/acoustic language interface. LSLT will then be put to use to show how discourse relations are mapped automatically from text using the tools available in the 4 sub-theories, and in particular we will focus on Causal Relations showing how the various sub-theories contribute to address different types of causality.