Vocabulary Knowledge for Proficiency in English as a Second Language – A Literature Review

Vocabulary knowledge is fundamental to language development, learning, and use. It is commonly held that without sufficient vocabulary knowledge, little can be communicated effectively in a language. However, in the English as a second language context, knowledge of vocabulary, the vocabulary size that guarantees high language proficiency, and how it is measured, remains scattered in individual studies, hence unclear to many researchers, teachers, and language learners. This paper reviews studies on vocabulary knowledge necessary for proficiency in English as a second language. The aim is to synthesise, analyse, and provide a comprehensive picture of the scholarly development of vocabulary knowledge and language proficiency research in L2 learning of English. The Protocol, Search, Appraisal, Synthesis, Analysis, and Reporting (PSALSAR) methodology provides an analytical framework for this study. The study synthesises and thematically reports insights on vocabulary size and knowledge required for second language proficiency, and the various approaches/tools for measuring vocabulary knowledge in English as a second language. Findings reveal that 98% of lexical coverage, which translates into the most frequent 2000-word families, is sufficient for the comprehension of reading a variety of texts. For productive skills, the coverage of 4000–5000-word families is necessary for students’ speaking and writing skills. Relatedly, knowing a word means knowing its features, behaviour, and use in various contexts. To effectively measure vocabulary size, the Vocabulary Levels Test (VLT), Academic Word Levels (AWL), and Vocabulary Size Test (VST) are used. To measure deep knowledge of vocabulary, the Vocabulary Knowledge Scale (VKS), Word Associates Test (WAT), and Word Part Levels Test (WPLT) are commonly used. The understanding of the vocabulary knowledge requirements is crucial for setting vocabulary learning goals, designing curricula, and developing appropriate vocabulary learning materials.