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Is there any consensus as to how many words are in the average adult's vocabulary? Over the years, I've come across various factoids and blurbs online and in magazine articles that have made statements like, "The average adult has a vocabulary of 20,000 words."

And if there is a consensus, how was such a number arrived at? Is the "20,000 words" claim (or whatever it happens to be) just a guesstimate or are these numbers arrived at in a more mechanical and, ideally, reproducible procedure? Have then been any formal studies in this vein?

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Once I wrote a spelling correction program, and its dictionary turned into a finite-state-machine. There are base words, but then there are common prefixes and suffixes, and even recursive suffixes, as in "nation", "national", "nationalize", "nationalization", "nationalizational", so defining what is even meant by vocabulary size is not straightforward. (And as "straightforward" shows, words can consist of other words joined.) –  Mike Dunlavey Sep 1 '11 at 18:39
The average English/US/Australian adult? –  user unknown Sep 1 '11 at 19:32
There doesn't appear to be a claim anywhere here (outside of the OP). It appears that this is just a random curiosity and desire to have an answer to "What's the average adults vocabulary". –  Russell Steen Sep 1 '11 at 23:35
Cheap joke: a cunning linguist once informed me that size did't matter.... –  Monkey Tuesday Sep 2 '11 at 2:04
People have several different vocabularies. There's the set of words they would use in speech, the set they would use in writing, the set they would recognize in speech, and the set they would recognize in writing. Without knowing what vocabulary is meant, it's not possible to answer this question (unless the idea is that the average adult has X many words in one of his or her vocabularies). –  David Thornley Sep 3 '11 at 1:57
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migrated from english.stackexchange.com Sep 1 '11 at 16:27

This question came from our site for linguists, etymologists, and serious English language enthusiasts.

4 Answers

Short answer: NO


There are a few problems with using a dictionary to estimate vocabulary size which Thorndike pointed out as early as 1924 in The Vocabularies of School Pupils. In short, using a dictionary will always result in an overestimation, and using bigger dictionaries will lead to even larger overestimations. This phenomenon is known as the big dictionary effect.

The testyourvocab site runs into related problems. Word selection is based on headwords, leading to the dictionary-based problems noted above. It also fails to use pseudowords to compensate for humans' uncanny ability to overestimate their own ability, a.k.a. illusory superiority. The inclusion of pseudowords on a checklist (yes/no) test is generally considered (e.g. Eyckmans (2004) Measuring receptive vocabulary size) to be the only way to make the test reasonably reliable because it ensures that a minimum level of word knowledge is enforced when claiming knowledge (i.e. one can really identify the form of the word).

There are other problems. Which level of word knowledge do you set as the cut off point for accepting that a word is part of someone's mental lexicon? Simply form identification (I've seen it before, but I have no idea what it means)? Full productive use (I can use this word appropriately in any context without hesitation)?

The project at vocabularysize.com is attempting to refine measurement techniques as well as establish norms. One unique aspect of this project is that they are trying to measure different aspects of word knowledge separately and then later combine them to come up with a more accurate measure of vocabulary size. For example, when testing the word nation, most people would assume that national, nationalistic, antirenationalisation, etc are also known because of normal morphological processes involved in creating the related words. However, morphological awareness grows just as vocabulary size does.

Here's an unlikely example to illustrate: if two people know the same 5,000 base words, the one with the ability to recognise the most common 100 affixes in English is going to have a smaller vocabulary size than the one who knows the most common 200 affixes in English. This is an oversimplified example because it implies that measuring word types (unique forms) is more valid than word families (base word + inflections + derivations), which is not a particularly useful way of measuring, but you get the idea. One's mental lexicon can't be measured just in terms of 'how many words'. It must be measured by looking at a variety of aspects dealing with knowledge of form, meaning, collocation, register, syntactic roles & constraints, etc.

So, to answer your question directly, no. There are too many problems defining concepts such as word and know to confidently state something like "There are x number of words in your vocabulary". What is more likely is to rate someone's vocabulary abilities, in terms of recognising various aspects of word knowledge or using those aspects productively, against age-based norms. There's also interesting work in psycholinguistics with reaction times in lexical decision tasks which hint at the interconnectiveness of one's mental lexicon which could also be used to rank subjects. Both approaches, though, would be more akin to standardised test scores which serve to rank rather than measure absolutely.

how was such a number arrived at?

There are a variety of methodologies, most centred on sampling from dictionaries which is unreliable. Despite early knowledge of this problem (Thorndike 1924), vocabulary size tests which have sprung up over the last 100 years have often tended to use this methodology. This is one reason why there are so many estimates which vary so widely.

A good overview of the issues involved in accurately measuring vocabulary size can be found in Nation, I.S.P. (1993) Using dictionaries to estimate vocabulary size: essential, but rarely followed, procedures. Language Testing, 10(1), 27-40. The most important points are that great pains must be taken to avoid oversampling from higher frequency words which tends to happen when using dictionaries as a source.

Is the "20,000 words" claim (or whatever it happens to be) just a guesstimate or are these numbers arrived at in a more mechanical and, ideally, reproducible procedure?

Some tests are more rigorous and valid than others. Measuring the vocabulary size of infants and very small children, for example, has seen very good gains in precision and accuracy, mostly because a fairly complete list of all words they could possibly know can be constructed. This becomes impossible as one learns more words. Most claims of adult vocabulary size are based on reproducible procedures, but the variance in estimates can usually be traced back to differences in defining the concept of word and the level of word knowledge tested. Remember, early IQ tests were basically vocabulary size tests, so there are many attempts out there which have norms, validation studies, etc. Many of them are quite useful as a ranking or discriminating measure, but are less useful to answer the more academic question of absolute vocabulary size.

Have then been any formal studies in this vein?

Yes, lots. Some of the first were:

  1. Holden, E. S. (1875). On the number of words used in speaking and writing. Bulletin of the Philosophical Society of Washington, 2, 16-21, 28.
  2. Kirkpatrick, E. A. (1891). Number of Words in an Ordinary Vocabulary. Science, 18(446), 107–108.

Other important studies include:

  1. D’Anna, C. A., Zechmeister, E. B., & Hall, J. W. (1991). Toward a meaningful definition of vocabulary size. Journal of Reading Behavior: A Journal of Literacy, 23(1), 109-122.
  2. Dupuy, H. J. (1974). The rationale, development and standardization of a basic word vocabulary test. US Govt Printing Office, Washington DC.
  3. Schonell, F. J., Meddleton, I. G., & Shaw, B. A. (1956). A study of the oral vocabulary of adults. Brisbane: University of Queensland Press.
  4. Seashore, R. H. (1933). The measurement and analysis of extent of vocabulary. Psychological Bulletin, 30, 709-710.
  5. Seashore, R. H., & D., E. L. (1940). The measurement of individual differences in general English vocabularies. Journal of Educational Psychology, 31, 14-38.

I've got a list of 30-40 studies, so I won't bore you with the rest.

In closing, perhaps the reason why measuring vocabulary size and debates about it have persisted for so long is that early IQ tests were essentially vocabulary size tests and people still tend to equate knowledge of arcane or obscure words as a sign of intelligence or other socially desirable traits. Although there is some correlation between vocabulary size and other traits, the strength of that correlation is often not as strong as people would assume, and it also doesn't imply any sort of causality.

Full disclosure: I'm part of the vocabularysize.com project

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An interesting, if not humbling, website. I took your test and was told I know significantly fewer words that are typically known by native speakers (13,700)! Eep. –  Scott Mitchell Aug 31 '11 at 0:21
@Scott Please note that neither of the tests on that website are mine. They were created, piloted, and validated with people I work with, but I just work on the website part. Also, you shouldn't be humbled at all. Flip a coin. Half of the population will be above average, half below. As I tried to point out above, a measure of raw size is relatively useless and imprecise, and getting a higher or lower score doesn't make someone more or less of a native speaker any more than knowing more or less Perl makes someone more or less of a programmer. –  myqlarson Aug 31 '11 at 0:26
I know, it's just hard not to be a tad bit taken aback when you score only better than 18% of the respondents and you fancy yourself to have what you consider to be an above average vocabulary! :-) –  Scott Mitchell Aug 31 '11 at 2:47
@Scott Most people think they are above average (illusory superiority), especially in Lake Wobegon. But the point is, these measures of size are extremely rough, almost to the point of being meaningless on their own. You also have to consider that technical vocabulary can't really be accounted for in a test like this, so if your self-appraisal is partially based on your relative balance of general to technical vocabulary, then that could show up in the test as being much lower than it actually is. All of this supports my answer to your original question: no. –  myqlarson Aug 31 '11 at 2:53
I think the vocabulary of any native speaker is enormous and it changes with the context. You probably can't ask a person sitting in front of a test to access his/her whole vocabulary providing a simple example of usage as context/stimulus. –  elcodedocle Apr 8 at 19:30
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The folks at testyourvocab.com are trying to find out just that. You don't have to fill out their test. The FAQ and the details page cover what you're looking for.

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I will add that several members of the ELU community have taken the test and the results ranged between 14,400 and 42,300 words for native speakers, and between 25,000 and 34,400 words for non-native ones. The variance was large enough to render any average number utterly useless. –  RegDwight Aug 1 '11 at 1:46
Nice link, except that the spousal unit edged me out. My ego is mortally wounded. –  dmckee Aug 1 '11 at 3:29
@dmckee - Tell her that it's not the size of your vocabulary that matters, but rather how you use it. :-) –  T.E.D. Aug 31 '11 at 14:48
unfortunately the methodology at this site is unsound. –  myqlarson Aug 31 '11 at 15:36
@myqlarson: I agree. However, vocabularysize.com was not good either for my range. They asked me to check again in a few months. Most questions seemed to be about very simple words. –  prash Aug 31 '11 at 16:10
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As others have said, much depends on your definition of "a word". The 250,000+ "words" in Collins Official Scrabble Words, probably represent a little over 100,000 "base words", with the rest accounted for by a small set of standard regular inflections. OSW doesn't include "uninflected" words of 10 letters or more - but although English includes a lot of these, they're mostly compound words that can be understood by deconstruction into meaningful sub-components.

Sticking to "base words", my understanding is you only need about 3000 to get by in terms of being able to express yourself without great difficulty, but even relatively illiterate people probably have more than twice that number at their disposal, so you'd often have difficulty understanding others' speech or writing with such a poor vocabulary.

I think the average person probably has a productive/expressive vocabulary (words they're likely to actually use) of 15-20,000 words, with a receptive/listening vocabulary (words they would understand, but not normally say/write) at least half as big again.

I can't resist adding that about 20 years ago I was commissioned by Roger Prebble (then managing editor of a major UK puzzle publishing company) to write crossword-generating software. He'd previously compiled a number of "word list" books published by Chambers, and as a goodwill gesture they'd allowed him free use of an electronic copy of Official Scrabble Words (UK rights to which they owned at the time).

Roger initially thought that being able to incorporate the OSW list into my program would be a major help. In the event, we soon realised that most of the words were so obscure they could never be used. He and a few others with exceptionally wide vocabularies had to spend many, many hours leafing through the list deleting anything they'd never heard of. Even of the 80,000 that remained after this savage cull, more than half were flagged as "very difficult", and not to be used by my program for "ordinary" puzzles. As far as I recall, we only marked about 10,000 as "well-known enough to be used in any crossword puzzle".

Just to put some context on that, bear in mind that most people who do crosswords at any level probably tend to have at least an "average" vocabulary, or they'd soon get frustrated and give up the pastime.

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I reckon this site states it pretty well:

Nagy and Anderson (1984) estimated that an average high school senior knows 45,000 words, but other researchers have estimated that the number is much closer to 17,000 words (D'Anna, Zechmeister, & Hall, 1991) or 5,000 words (Hirsh & Nation, 1992). Surely these dramatically different estimates depend upon the three questions described above, namely, what does it mean to "know" a word, what counts as a "word," and who counts as "average?"

We can't really make a definite statement about this. The statistics provided in the magazines and stuff are only estimates.

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