Estimates of the size of adult vocabularies vary widely both within and across languages. For example, estimates of the vocabulary size of young adult speakers of American English range from 30,000 to 100,000 depending on the resources used to make the estimate and the definition of what it means to know a word. What is agreed upon is that the vast majority of words that mature speakers use in their dayto-day interactions are acquired early in life through spoken interactions in context with care givers and peers, usually well before the start of formal schooling. This active vocabulary is extremely limited compared to the size of the adult vocabulary (usually on the order of 2000 words for young speakers) and is quite stable, with very few additional words learned via casual conversation beyond this early stage. Obviously, this leaves a very large number of words to be acquired by some other means.