Figure 2.1 proposed by Pikulski and Templeton (2004, p. 2) demonstrates that
vocabulary items play a dominant part in learning to communicate effectively while
listening, speaking, reading, and writing. Vocabulary items in the diagram above can
be classified in terms of types, meanings, and functions. Based on the diagram,
vocabulary is categorised into four main groups as meaning/oral vocabulary,
literate/written vocabulary, receptive vocabulary, and productive vocabulary.
However, it is obvious that all vocabulary items are overlapped in meanings and
functions.