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Incidental vocabulary learning Acquiring words unintentionally

This page describes incidental vocabulary learning, giving information on what incidental vocabulary learning is, why it is important, and how much repetition is needed to learn words. There is also information on incidental vocabulary learning for academic and technical vocabulary.

In a separate section there is a tool to calculate likelihood of incidental learning for words in two major lists: the Academic Word List (AWL) for academic words, and the Secondary School Vocabulary Lists (SVL) for technical words.

What is incidental vocabulary learning?

Incidental vocabulary learning generally refers to learning words as a result of reading a wide range of books or other material for pleasure (also called extensive reading), during which there is no explicit intention to learn words, though words are often learned as a byproduct (Webb, 2020a). Incidental learning can also occur as a result of watching TV and films (extensive viewing) or listening to podcasts or other recordings (extensive listening).

Incidental vocabulary learning is often contrasted with intentional vocabulary learning, which uses flash cards, gap fill exercises, matching exercises and other strategies to explicitly focus on learning words (Webb 2020a).

Why is incidental vocabulary learning important?

While incidental vocabulary learning accounts for the majority of the vocabulary learned in one's first language, research suggests that for a second (foreign) language, intentional vocabulary learning is responsible for most of the vocabulary learned (Webb, 2008). Incidental vocabulary learning is still important, for two main reasons.

First, the number of words required for comfortable reading or listening is too large to be learned through intentional study alone. It has been estimated that for comfortable reading, knowledge of 8000-9000 word families is required, while for listening the figure is 4000 word families (Webb, 2020a). This number is too great for intentional vocabulary learning alone.

Additionally, intentional vocabulary study tends to focus on meaning only. In contrast, incidental vocabulary learning through repeated exposure to words via extensive reading, viewing or listening is likely to build up detailed knowledge of form, meaning and use of words, including aspects such as collocation (Webb, 2020a). In other words, incidental vocabulary learning leads to richer knowledge of vocabulary.

As such, intentional and incidental vocabulary learning should be seen as complementary to one other, rather than competing or contrasting vocabulary learning strategies.

How much repetition is necessary?

There is no 'magic number' of times a word needs to be read (or heard) before it is learned. Studies have variously suggested 6, 8, 10, 12 or more than 20 encounters may be needed (Uchihara, Webb and Yanagisawa, 2019). A study by Webb (2008) showed that while increasing the number of encounters led to increased knowledge of form (i.e. spelling), a more important factor for learning meaning was the context, in other words how clear the meaning of unknown words was, and this may account for the difference in numbers mentioned above, since the more difficult it is to guess the meaning of an unknown word from context, the more times it needs to be read or heard before it is learned.

Incidental academic vocabulary learning

One definition of academic vocabulary is words which occur more frequently in academic texts than in general English texts. Coxhead (2000), when devising the Academic Word List (AWL), found that it covered around 10% of words in academic texts, but only 1.4% of words in non-academic texts. This implies that it is difficult to learn academic words through extensive reading, viewing or listening. However, this is precisely how students whose first language is English learn most such words, and with enough exposure, second language students are likely to encounter many if not most academic words, such as those in the AWL, through reading, viewing or listening for pleasure. Although technical words are even more likely to be low frequency in nature, there may still be sufficient opportunities to encounter many of them in non-academic texts.

A recent study by Clarence Green (2022) computed how much time would be needed to encounter words in the AWL (for academic words) and the SVL (Secondary School Vocabulary Lists, for technical words), via extensive reading or extensive viewing, with 6, 12 and 20 repetitions, based on their frequency in a corpus of reading and a corpus of viewing texts. With a moderate reading rate of 200 words per minute (wpm), AWL words such as found, final, job, couple, respond, ignorant, and area could all be encountered at least 6 times within 4 hours of reading, 12 times within 8 hours of reading, and 20 times within 13 hours of reading, all easily manageable with 30 minutes of reading per day over the course of eight days (4 hours) to a month (15 hours).

Similarly, AWL words such as issue, percent, secure, economy, military, investigate, media, and obvious could all be encountered 20 times within 6 hours of viewing (for a viewing rate of 140 wpm).

Conversely, words such as intermediate, whereby, paradigm, empirical, concurrent, aggregate, and qualitative would all need over 600 hours of reading and over 200 hours of viewing to encounter them a minimum of 6 times, in other words around 2 hours of reading per day for one year, or 2 hours of viewing per day for 4 months, which may be more time than students of academic English have available during their course of study.

Green's study found that all of the 570 words in the AWL were present in the reading and viewing corpuses, though some only appeared once. However, several technical words (from the Biology, Chemistry, Physics and Maths lists used in the study) were not present, meaning that these are very unlikely to be learned through extensive reading or viewing.

The information from this study gives students (and teachers) a clear idea of which academic words (from the AWL) and which technical words (from the Biology, Chemistry, Physics and Maths lists of the SVL) are likely to be learned through incidental vocabulary learning, and which ones will need intentional vocabulary learning such as via explicit instruction in class.

There is a tool based on this research on a separate page, that can be used to calculate which words in the AWL and SVL (Biology, Chemistry, Physics and Maths lists) are likely to be learned by extensive reading/viewing in a given time frame.


Coxhead, A. (2000) 'A new academic word list', TESOL Quarterly, 34(2), 213–238.

Green, C. (2022) 'Computing curriculum time and input for incidentally learning academic vocabulary', Language Learning & Technology, 26(1) 1-21.

Uchihara, T., Webb, S., and Yanagisawa, A. (2019) 'The effects of repetition on incidental vocabulary learning: A meta‐analysis of correlational studies', Language Learning, 69(3), 559–599.

Webb, S. (2008) 'The effects of context on incidental vocabulary learning', Reading in a Foreign Language, 20(1), 232–245.

Webb, S. (2020a) 'Incidental vocabulary learning', in S. Webb (Ed.) The Routledge handbook of vocabulary studies (pp. 225–239). Routledge.

Webb, S. (2020b) 'Introduction', in S. Webb (Ed.) The Routledge handbook of vocabulary studies (pp. 1–12). Routledge.

Next section

Check out the tool for calculating likelihood of incidental vocabulary learning (for AWL and SVL words) in the next section.


Sheldon Smith

Author: Sheldon Smith    ‖    Last modified: 23 July 2022.

Sheldon Smith is the founder and editor of He has been teaching English for Academic Purposes since 2004. Find out more about him in the about section and connect with him on Twitter, Facebook and LinkedIn.

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