Are there 20,000 English words in the average adult's vocabulary?

Question

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?

Answer 1

Short answer: NO

Details:

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

Answer 2

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.

Answer 3

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.

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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.

Answer 4

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.

Answer 5

It is within the range of 35,000–75,000 depending on your level of learning, so a better number would be 50,000.

Underestimates

Part of it is going to depend on what you consider to be your vocabulary. Do you only count words you use on a regular basis and know thoroughly, or does a word you might only scarcely recognize once you see it count? It is typically established 90% of English you might use or encounter on a daily basis comprises of just 3,000 words, and these 3,000 words are of special interest to E.S.L. studies. However, some very common words that people would consider a regular part of their vocabulary do not exist within these 3,000 words. As a native speaker of the English Language, I would suppose that almost any other native speaker above 5 years of age should recognize the word frown, but it is not listed in the Longman Communication 3000, which is a list prefaced by the claim that these 3,000 words are the 3,000 most commonly occuring words based on analysis of a 390 million word corpus and constitute 86% of the words used. The Oxford 3,000 does not have it either.

Part of it is going to depend on what you determine to be a single word and the Test Your Vocab website is using a very conservative definition and that skews their numbers towards the lower bound. They only count headwords, and not derivations. They would count quick as a word, but not quickly because it is just a derivation of the word quick with a predictable change in signification. Maybe some scholars would find this a reasonable restriction, but I for one do not.

Test your vocabulary also chose to omit technical specialist terms from the test simply because they lack general applicability. I for one do not consider these to be sound criteria, nor would Samuel Johnson as he explained in A Plan for An English Dictionary. Notably he states:

The academicians of France, indeed, rejected terms of science in their first essay, but found afterwards a necessity of relaxing the rigour of their determination; and, though they would not naturalize them at once by a single act, permitted them by degrees to settle themselves among the natives, with little opposition; and it would surely be no proof of judgment to imitate them in an errour which they have now retracted, and deprive the book of its chief use, by scrupulous distinctions.

Now the Test Your Vocabulary test certainly includes many challenging words in the commonly shared vocabulary that would test the limits of anybody's knowledge, but they might gloss over many perfectly legitimate words due to simple obscurity, and cut off the results at an estimated 45,000 words.

So again, the test your vocabulary estimate is probably too low and their summary of results on May 10th 2013 suggest that the average speaker knows 20,000–35,000 words. Therefore, the actual number should be greater than that.

The Upper Bound and Typical Estimate

A far more usual estimate is 35,000–75,000, depending on the level of the speaker's learning. This is the range given by Professor David Crystal as cited in the B.B.C. News Magazine article Words in the Mental Cupboard which was written by Caroline Gall and published on their website on April 28th 2009. Professor Crystal supposes that the size of a typical vocabulary is around 50,000. Another source which makes this claim is Improve Your Speed Reading by Phil Chambers, which claims there was a joint google/harvard study on the matter of vocabulary size. I believe these numbers to be accurate because we have concrete evidence that the upper bound is achievable in the form of historical dictionaries.

According to Peter Sokolowski, editor at large for Merriam-Webster, the 1864 edition of their Dictionary was "the first dictionary in English created by a large staff", so before then we can presume that they were principally the work of one man. According to the Noah Webster House & West Hartford Historical Society:

Webster’s greatest achievement was the dictionary. In 1800 he published his intentions of writing a dictionary. He published a shortened, concise but comprehensive, version in 1806. The final version was finished in 1825 and published in 1828. It contained 70,000 words.

This information is somewhat misleading. The A Compendious Dictionary of the English Language (1806) may have lead to the creation of An American Dictionary of the English Language (1828), but they were distinct works.

However, the word count is probably correct, or if not a close enough estimate. I know this because in the past, I had run a wildcard search on A.R.T.F.L. project, which returned somewhere around 65,000 words, and like most of the online transcriptions it had some glaring omissions that are included in a hardcopy, such as the usual form of rank. You will not be able to verify this with them directly, since A.R.T.F.L. Project seems to have taken down the resource, but there is a hardcopy fascimile of the original (albeit bound in one volume) published by The Foundation of American Christian Education, with the I.S.B.N. of 978-0-912498-03-04 if the especially skeptical among you would like to verify my claim with a hand-count.

Granted, An American Dictionary of the English Language has some questionable inclusions which may inflate the number, such as compounding loving-kindness as a single world. Also, Webster was not entirely without aid, as he had help from Emerson Worcester and his Son in Law. However, on the other hand, this was during the early 19th century so he had fewer learning aids and an aacessibility handicap, and An American Dictionary of the English Language was the largest at the time of its initial publication, containing 12,000 words that were not published in prior dictionaries, which is over half of the 20,000 count mark alone.

These will not all be all of the words you use on a daily basis daily, and since a dictionary acts as a record it may not even be representative of all of the words you might be able to recognize off of the top of your head. However, what this does prove is that learning roughly 75,000 words is an accomplishable feat with dedicated study, lending credit to the notion that a people have the capacity to learn 20,000 or more words.

This lends credit to the notion that the numbers given by Professor Crystal and the joint Google/Harvard study are indeed accurate, at least under the provision that their definition of what constitutes a "word" is reasonable, since their upper bound roughly matches that which has been actually been documented by a famously learned man.

However it also gives us reason to cast doubt that any estimate of the average above or even approaching 75,000 words is reasonable, given that Webster dedicated 25 years to creating his dictionary in addition to whatever pre-existing knowledge he had. It is true we have better learning tools and greater accessibility to information than we did in the 19th century, but not very many individual people spare 25 years of their life to the sole task of compiling words, and there is less motivation to do so since the practice of independent lexicography has effectively stopped.