The document provides an overview of various linguistic theories and their implications for language teaching, including: 1. Classical/traditional grammar focuses on the role of words in sentences, while structural linguistics describes grammar through sentence structures. 2. Transformational generative grammar examines deep and surface language structures and meanings. 3. Functional/notional approaches analyze language in terms of social functions and intentions rather than form. 4. Discourse analysis looks at language use beyond the sentence level and how meaning is constructed between sentences. 5. Different linguistic theories may be more relevant for describing certain features of specific languages.