How can our teaching help our learners to acquire vocabulary? If left to incidental learning, it takes a long time, but our students are often operating under quite severe time constraints. They may be taking up a language ab initio during their first year at university, for example, and need to achieve degree-level competence in this language in their final year. Explicit study is therefore essential for these students if they are to acquire a sizeable working vocabulary. Research shows they need to pass a certain barrier, a size threshold, that enables them to begin reading authentic texts, somewhere between three and five thousand word families (Laufer and Nation, 1995; Nation and Waring, 1997). In addition to explicit work on vocabulary, an effective way of to achieve this is to increase the amount of exposure. Elley (1991), working in the South Pacific, taught vocabulary by a book flood method, where students merely read or were read to extensively, with no explicit supplementary exercises that focussed on linguistic analysis. These students achieved greater language proficiency than a control group who were learning vocabulary via an audio-lingual method, during a similar period of instruction. We are learning a great deal now from corpus linguistics about how second language competence develops. (See Biber, Conrad and Reppen, 1998, for an interesting study on language acquisition and development via corpora of student written and spoken texts.)

It is important to familiarize meaning before form, as was done in Activity 7. We know, from child language acquisition studies, that meaning is acquired in three broad stages: labelling a concept, categorizing a number of items under this label, and then building networks between items (Aitchison, 1987). Children may at first, for example, name every vehicle travelling past their house 'car'. Later they learn to distinguish 'bus', 'tractor', 'bicycle' from 'car', as they become exposed to and notice these terms. Subcategories of 'car', perhaps in terms of brand names or of shape, also emerge, and, with subsequent exposures, the meaning boundaries become familiar, allowing children to categorize new items successfully.

Meaning boundaries may be problematic to set for second language learners, especially if concepts have no equivalent in the native language. For example: 'lend' and 'borrow' denote separate concepts in English but not in many other languages; French is similar to English in having one term for 'tree' (arbre), one term for 'wood' (bois), both as material and as small forest, and one term for 'forest' (forêt), but other languages have only two terms to cover these three concepts.

The following activity shows vocabulary acquisition at work in mother-child, and teacher-student contexts. The former takes place in a natural home setting, whilst the latter takes place in a classroom. You may like to reflect on the occurrence and the nature of 'exposure' and ' explicit instruction' in both extracts.

Activity 8

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