Though I’m not sure whether this question is suitable to EL&U site or not, I’m glad if I can get any input on the relationship of the vocabulary and comprehension of English language, or if you can suggest me other suitable site that I can post this question.

I recently read the book, titled “Read a Million Words (to master English language),” written by Japanese English language scholar at Tokyo Tele-communication University, Kunihide Sakai.

Mr.Sakai cites the following numbers:

  • Vocabulary of 1,000 words allows 80% comprehension of English statement

  • 2,000-word vocabulary allows 86.6 % comprehension of English statement

  • 3,000-word vocabulary allows 90.6 % comprehension of English statement

  • 4,000-word vocabularies allows 92.8 % comprehension of English statement

Though it’s not clear what "English statement" means (maybe I’d do better to ask him directly as well as about the source of number), it’s hardly believable that 3,000 vocabulary level allows 90% comprehension of general statement in English language from my experience of reading English language literatures everyday to look for the subject for posting EL&U.

I know British psychologist and linguist, Charles K. Ogden asserted that we can express everything we want to say with 1,500 words (850 basic English words and their combinations, plus 350 international (foreign) words and 300 from scientific terminology), and promoted Basic English movement during 1930s.

Winston Churchill supported Ogden’s theory and recommended diffusion of Basic English as the international language in his discourse at Harvard University in 1944. However, Ogden's theory is applied only to writing and speaking, not reading and hearing.

Is there any trustworthy study that illuminates the relationship between vocabulary level and ability to comprehend English language statements expressed in day-to-day conversation, literature (not too academic) and daily journals? What is its finding with regards to the relationship between vocabulary and comprehension?

  • I think this is a bit not constructive for the main site because you're asking for a list. However, pop on in to chat--I'm sure people have read studies of this sort and could point you in the right direction.
    – simchona
    Dec 5, 2012 at 1:19
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    The question only needed the barest editing to make it more objective, which I have done. I think this is an interesting and answerable question and deserves to be reopened. Dec 5, 2012 at 4:00
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    Any such enterprise is fraught with difficulty. What is a word? What is comprehension? These have to be very tightly defined for any results to make any sense. Dec 5, 2012 at 10:39
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    @Yoichi: I hate having to vote Not Constructive on any of your questions, because they're always interesting! I doubt I can really add much to jwpat7's comprehensive answer, but I would just say I think if two people both had perfect knowledge of the same 4000-word vocabulary (or even considerably less), they could in principle achieve 100% for both "expression" and "comprehension". They might sometimes have to use more words to express certain concepts, is all. Dec 7, 2012 at 22:33
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    Oishi-san, I think this is like those books that tell you you can achieve basic literacy in Japanese by knowing only ~1,000 漢字. Even knowing all the characters in the 常用漢字 doesn't make one anything like completely literate. There are many more characters, words, proper names, 熟語, and 外来語 that native speakers know without even thinking about it, which the casual student would find utterly opaque.
    – Robusto
    Dec 8, 2012 at 1:27

1 Answer 1


A person who has a large vocabulary does not necessarily comprehend a higher fraction of all statements than a person with a small vocabulary; that is to say, some people with small vocabularies may understand what people tell them or what they read more quickly and thoroughly than other people with large vocabularies. But it is reasonable to suppose that on the average, and as a general rule, larger vocabulary leads to better understanding.

The trend expressed in the quoted statistics is of plausible form: the first thousand words counting for most understanding, with successively lower return from each increment thereafter.

As to whether a 3000-word vocabulary level typically allows 90% comprehension of general statements in the English language (where, as noted in comments, word and comprehension are nebulous concepts), I find the statistic both plausible and implausible, believable and unbelievable. In favor of the statistic, the vocabularies of typical American English speakers that I encounter seem quite limited; toss out any word not among the top few thousand words and they don't know the meaning of it. Strongly weighing against the statistic are webpages as at testyourvocab.com which shows about 3300 words in the vocabulary of the average 3-year-old, and 20000 to 32000 words in the vocabulary of average people older than 15. A straightdope.com page quotes Stephen Pinker as suggesting the average American high-school graduate knows about 60000 words. In his book The Language Instinct, Pinker says the 45000-word average vocabulary suggested by other researchers rather underestimates vocabulary size.

To recapitulate: (1) vocabulary size is not necessarily a good predictor of language comprehension; (2) nothing in this answer either establishes or disproves any of the statistics mentioned in the question; and (3) I think the terminology in the question is not precise enough to allow definitive answers.

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    +1 Very well explained points. There could have been some reference to any actual studies, with citations. The discussion in the answer mainly concerns with people's vocabulary strength and not vocabulary application. This is an important distinction. OP's question relates to the vocabulary required to correctly understand the average statement. The references in your answer, on the other hand, relate to how many words a person knows. They are different concepts. It is known that in regular reading, a person rarely ever uses some (like 20-30 per cent?) of the words he knows.
    – Kris
    Dec 6, 2012 at 6:14
  • @Kris, I agree with most of the points in your comment and agree the distinction is important. Note, I don't know if “vocabulary required to correctly understand the average statement” can be determined; what can be measured (or estimated) are vocabulary size of participant and participant's level of understanding. I didn't find much about levels of understanding. Dec 6, 2012 at 6:24

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