Toward a Meaningful Definition of Vocabulary Size

Studies using dictionary-sampling methods to estimate vocabulary size have left a bewildering trail of widely differing estimates. We argue that many estimates are misleading (generally too high) principally because the definition of a word is too liberal. For practical purposes (e.g., planning vocabulary instruction), it makes sense to define a word as a base form, resembling what linguists call a lemma, and to disregard certain word forms from estimates of vocabulary size (e.g., proper names and archaic words). By providing a clear rationale for the word source which was sampled, and by using clearly defined operational criteria for what constitutes a word as well as for the procedures used in the estimation task, we found that the average number of different words known by a college student is 16,785. We suggest that vocabulary size, and corresponding rates of vocabulary growth, may not be as great, nor attempts to directly teach vocabulary as futile, as some would suggest.