It is not. Vocabulary is far from the binary of "you know this word or you don't". At a minimum, it is usually split into passive and active vocabulary, with pa

It is not. Vocabulary is far from the binary of "you know this word or you don't". At a minimum, it is usually split into passive and active vocabulary, with passive being the words you understand when encountered, and active being the words you can use effectively. Wikipedia's entry is a pretty good overview.