How Many Words and Sentences Do We Know?

You probably hardly pay any attention to it, as it is natural to us. You are doing it right now and you are very talented at it. You also do it when you talk on the phone. When you hang out with your friends. When you read the newspaper. When you watch the news. It is this surprising talent that any human acquires when we are only a few years old. From then on, we rapidly get better at it, until we truly master the skill.

That talent is called language processing. The talent of speaking, listening, reading, and writing. Many excellent articles and books have been written about this talent. And yet, one very simple question—how many words and sentences do we know—has not quite been answered, perhaps because the answer turns out to be so difficult.

There are, of course, a range of factors that we should take into account when answering that question. You may ask: Do you mean for one language or for multiple languages a person speaks? Do you mean producing language in speaking and writing, or do you mean comprehending language? And does the answer not depend on age? These are all valid questions, but let’s simplify the question as much as possible and focus on approximately how much of the English language we comprehend.

In 2016 colleagues of mine designed a clever experiment to get to the answer. They gave 221,268 participants in an experiment a list of words and were asked to indicate whether they knew these words. Of course, they wanted to avoid participants answering that they knew all of the words presented to them. So they got clever. Sixty-six percent of the words were actual words from the English language, but 33 percent were non-words. Nonwords like misk, molk and rontence. They looked like English words but were, in fact, not. On the basis of the error rate of participants, they were able to correct for guessing. Based on the findings corrected for guessing they estimated that 20-year-olds know about 42,000 different words, and 60-year-olds some 48,200 different words. Others have estimated that the number more lies in the range of some 60,000 words.

However, these words do not include multi-word expressions like peanut butter, car park, and traffic light (and knowing these words individually does not quite get you to the multi-word expression). They did not include names like Beyoncé, Facebook, or Washington either.

But. We. Do. Not. Read. Words. We read sentences. And that makes the answer to the question of how many words and sentences we know even harder. We cannot just assume that the answer to how many sentences we know is the number of combinations of all the words we know, 60,000 x 60,000 = 3,600,000,000 sentences. Answer sentence number combinations words, for instance, is not a sentence. We have to consider the grammar, the sentence structure that allows certain word combinations but not all combinations.

Let’s try to compute the numbers (bear with me). As a thought experiment, let’s first assume that we only have six words we know, rather than those 60,000 words. Let’s assume these six words consist of three nouns (John, Mary, and Jane) and three verbs (hits, beats, and hugs). From this rather limited vocabulary of six words and a sentence structure English has (noun verb noun), we can generate 27 different sentences (Mary hugs Jane, Mary hits John, Jane beats Mary being three of them). Because the sentence structure could also consist of a noun-verb combination (John hugs), the number increases to 36.

Okay, let’s take this to the English language at large. We happen to know that the average sentence length is 15-20 words; let’s assume that the sentences we know can be a maximum of 20 words. That a sentence is 20 words long is not quite true, because we can easily create sentences that are considerably longer than 20 words, such as this one. But let’s stick to 20 words in a sentence and assume that sentences can be three words, four words, and so on.

We also know that in the language we use, we use approximately 19 percent nouns, 27 percent verbs, 6 percent adverbs, 3 percent adjectives, 21 percent pronoun, 7 percent prepositions, and the remaining 15 percent consisting of determiners, coordinators, modals, subordinators, and adverbial particles. We can now estimate the number of nouns, verbs, adjectives, adverbs, and other categories in a three-word sentence, four-word sentence, five-word sentence, up to a 20-word sentence, our maximum sentence length.

Source: Ron Hyrons Shutterstock

Of the 60,000 words we know, we have about 14,400 nouns at our disposal, 16,800 verbs and some pronouns, which translates to over 30,000 noun, verb, and pronoun combinations. A 10-word sentence is then estimated to have two nouns, three verbs, one adverb, two pronouns, and one preposition. This means that the possible permutations of a 10-word sentence are over 4,741,000,000,000 sentences. If we now add the number of permutations from a three-word sentence to a 20-word sentence, we end up interpreting over 5,000,000,000,000,000,000,000 sentences. But so far we assume that the order of the word classes in a sentence remains constant. This is obviously not the case. Let’s simplify the situation again and assume that there are only two variations of word order in a sentence. If we only take two-word order variations into account, we can safely assume that we know at least 10,000,000,000,000,000,000,000 sentences or 10 sextillion sentences.

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How much that is? Well, let’s assume that an average daily newspaper has about 120,000 words and we estimate with some 10 words per sentence some 12,000 sentences. The number of sentences we know is the same as the number of sentences we experience when reading every second of our life—from birth until we die—8,500 newspapers. The next time you are at a party and people are bragging about the latest deal they closed, the car they bought, or the many miles they ran, you can brag too. You know as many sentences that are published in 8,500 newspapers every second of your life, some 10 sextillion sentences (don’t tell them that they themselves know that much too).

Before you object that it is unfair to count the number of words this way, let alone the number of sentences because once you know the rule system behind words and sentences one should not count words and sentences individually, you are right. But that’s not the point. The point here is to marvel at the impressive talent that we have that often goes unnoticed because it comes so naturally to us. Getting a sense of how many words and sentences we know, brings us to the question: How do we keep those words in mind. That’s a question I’ll save for a later post (and for a popular science book that will come out soon).