This paper argues that formal and explicit instruction and learners' prior knowledge play a crucial role in teaching and learning English as a second language (ESL), and that a pure communicative approach is inadequate in achieving optimum results. The discussion is presented in two parts. The first outlines the issues under consideration, including distinctions between foreign language learning and second language acquisition and between the communicative approach to second language instruction and explicit language instruction. It also examines the importance of prior knowledge in the cognitive process and the role of the native language in second language learning, drawing on theory and research in these areas. The second part presents the example of ESL learners of Chinese cultural background, focusing on the role of cultural differences in language learning. Specific linguistic differences between Chinese and English are considered, including the use and construction of indirect expressions, linear vs. circular thinking patterns, differences in intonation, and differences in verb tense and time reference. Contains 24 references. (MSE)