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Because experts disagree about what constitutes a word, it is difficult to count the number of words people know. The simple word run, for example, can be transformed by adding suffixes to produce the nouns runner and running. Are these distinct words? Furthermore, run has many meanings. Does each meaning count as a different word?
Estimates of an individual’s word knowledge must also consider the difference between active vocabulary — the words a person can use — and passive or receptive vocabulary — the words a person can recognize or understand in print or when other speakers use them. The receptive vocabulary of native speakers and second language learners alike is much larger than their active vocabulary.
Some studies suggest that by the time they start Kindergarten, English-speaking children know about 1,000 words and add this total at the rate of about 1,000 words a year. By the age of eight, most students have a vocabulary of 4,000 to 5,000 words. According to some estimates, the average undergraduate enrolling at university has acquired a vocabulary of about 15,000 word families, which are related words such as educate, education, educated and educational.
In text 9A2DDD, in the clause “Furthermore, run has many meanings” (R.5), the word “Furthermore” can be correctly replaced by