The method, part 1
Learning vocabulary through reading: what the research says
Most of the words you know in your first language were never taught to you. You picked them up from stories, conversations and books. Here is what decades of research say about learning a foreign language the same way, and how to do it efficiently.
Most words are learned from context, not from lists
A school curriculum explicitly teaches a few hundred words a year, yet children add thousands to their vocabulary. In a classic study, Nagy, Herman and Anderson asked students to read ordinary passages and then tested them on unfamiliar words they had met there. A single reading produced small but reliable gains1. Small gains per word add up fast when you read hundreds of thousands of words a year.
Stephen Krashen reviewed a large body of studies and came to the same conclusion for both first and second languages: vocabulary and spelling are acquired mostly by reading, not by drills2.
Reading also teaches what a word list cannot: which words go together (make a decision, not do a decision), the tone of a word, its grammar, and the situations it belongs to. Learners who meet a word more often in informative contexts gain more of these different kinds of word knowledge, not just its translation3.
The 98% rule: how hard should a book be?
If a text is full of unknown words, you stop understanding it and stop learning from it. In a well-known experiment, Hu and Nation varied how many words in a story were unknown and measured comprehension. They concluded that most learners need to know around 98% of the words to understand a fiction text without help4. That is one unknown word in every fifty, or roughly six on a typical page.
98% known words
90% known words
To reach 98% in ordinary written English you need about 8,000–9,000 word families5. Most learners are far from that, which is why graded readers and adapted texts exist. A 2023 replication with a larger group found the link between coverage and comprehension more gradual than a single cut-off6, so treat 95–98% as a useful guide rather than a hard rule.
What this means in practice: pick texts where you understand the story without translating. If you need a dictionary several times per paragraph, choose an easier text or an article at your level, for example in the graded reading catalog.
One encounter is rarely enough
Seeing a new word once leaves only a trace. Webb showed that learners who met unknown words more times gained significantly more knowledge of them3. In a study with an unmodified novel, Pellicer-Sánchez and Schmitt found that for words met more than ten times, readers recognised the meaning of 84% and could recall the meaning of 55% without any teaching7.
Even after ten encounters, almost half of the meanings could not be recalled. And most new words in a real book appear far fewer than ten times. Reading alone is a slow way to make a word stick.
Why reading alone is not enough
Readers also miss words. Hulstijn and colleagues found that learners often skip unfamiliar words or wrongly assume they know them; making the meaning available while reading, for example as a gloss in the margin, improved how many words they learned8.
Then there is forgetting. Without review, much of what you learn today will be gone within days. The good news is that forgetting can be slowed down with a simple technique: short reviews at growing intervals, which we explain in part 2: how to remember new words.
So the most efficient approach combines both: reading gives you words in context, deliberate review makes them stay.
How to learn vocabulary by reading: a practical method
- Choose the right level. You should follow the story without translating. Short articles at your level are a good start before full books.
- Do not translate everything. Look up words that block your understanding or keep coming back. Skip the rest; you will meet the important ones again.
- Check the meaning in context. A dictionary gives you all the meanings; the sentence tells you which one is used here. Idioms and set phrases must be translated as a whole.
- Save the words you look up. A word you looked up once and closed is a word you will look up again next week.
- Review in short sessions. A few minutes a day of active recall beats an hour of rereading lists.
- Keep reading the same author or topic. Words recur within one book or series, and every new encounter strengthens them for free.
How Booklex puts this into practice
Booklex was built around this research. You read your own EPUB and PDF books, classics from the free library or graded articles from A1 to C2. When a word stops you, tap it: the translation, meaning and pronunciation appear right on the page, so you keep reading instead of skipping. The Smart Translator reads the whole sentence, so idioms are translated as phrases, not word by word.
Every word you tap can be saved in one move to a list for that book. Booklex then brings it back at the right moments through five short exercises, so the words you met in your book become words you actually know. How that works is explained in part 2.
Frequently asked questions
How many words do I need to know to read a book in English?
For comfortable reading of ordinary fiction, research suggests knowing about 98% of the words on the page, which for general English means around 8,000–9,000 word families. You can start much earlier with graded readers, adapted articles or a reader that translates unknown words on tap.
Should I look up every unknown word?
No. Look up words that stop you from understanding the sentence or that keep repeating. Guessing from context is useful, but learners often guess wrong or skip words, so check the ones that matter.
Is reading better than flashcards?
They do different jobs. Reading shows you how words are really used and gives you many encounters; flashcards and other retrieval exercises make sure you can recall the words later. The combination works better than either alone.
When can I start reading books in the original?
Usually around B1, when you know the most frequent 2,000–3,000 words. Before that, short graded texts work better. With tap-to-translate you can read a level above your own, as long as you still follow the story.
Sources
- Nagy, W. E., Herman, P. A., & Anderson, R. C. (1985). Learning words from context. Reading Research Quarterly, 20(2), 233–253. 10.2307/747758
- Krashen, S. (1989). We acquire vocabulary and spelling by reading: Additional evidence for the input hypothesis. The Modern Language Journal, 73(4), 440–464. 10.1111/j.1540-4781.1989.tb05325.x
- Webb, S. (2007). The effects of repetition on vocabulary knowledge. Applied Linguistics, 28(1), 46–65. 10.1093/applin/aml048
- Hu, M., & Nation, I. S. P. (2000). Unknown vocabulary density and reading comprehension. Reading in a Foreign Language, 13(1), 403–430.
- Nation, I. S. P. (2006). How large a vocabulary is needed for reading and listening? The Canadian Modern Language Review, 63(1), 59–82. 10.3138/cmlr.63.1.59
- Kremmel, B., Indrarathne, B., Kormos, J., & Suzuki, S. (2023). Unknown vocabulary density and reading comprehension: Replicating Hu and Nation (2000). Language Learning, 73(4), 1127–1163. 10.1111/lang.12622
- Pellicer-Sánchez, A., & Schmitt, N. (2010). Incidental vocabulary acquisition from an authentic novel: Do Things Fall Apart? Reading in a Foreign Language, 22(1), 31–55. nflrc.hawaii.edu/rfl/item/207
- Hulstijn, J. H., Hollander, M., & Greidanus, T. (1996). Incidental vocabulary learning by advanced foreign language students: The influence of marginal glosses, dictionary use, and reoccurrence of unknown words. The Modern Language Journal, 80(3), 327–339. 10.1111/j.1540-4781.1996.tb01614.x
