This document discusses English for Specific Purposes and provides an overview of language descriptions and theories of learning. It covers six main approaches to language description: classical grammar, structural linguistics, transformational generative grammar, language variation and register analysis, functional grammar, and discourse analysis. It also discusses several theories of learning: behaviorism, mentalism, cognitive code, affective factors, learning vs acquisition, and models of learning. The conclusion states that while no single source or approach is perfect, teachers should recognize different approaches as ways to look at the same thing and choose methods that suit language descriptions and consider evidence from practice.