As you speed through the Challenge, watching the words you’ve learned accumulate like so many dollars in the savings account of life, do you ever stop and wonder how many words are out there?

You might have an easier time counting the stars in the heavens. Even linguists and lexicographers can't agree on a number. (And many believe the search for one is a bit silly.) 

"It's really an unanswerable question," says lexicographer Ben Zimmer, who contemplated this issue in his Word Routes column Powers of Ten. The 20-volume Oxford English Dictionary, for instance, includes entries for about 250,000 words, though its editors by no means suggest that this number represents the English lexicon. "You can expand the number in any direction you like," Zimmer explains. "There's technical words, foreign words, or slang, to name a few."

Fortunately, as vocabulary learners, we don't need to be as concerned with the question of how big the lexicon is as we do with the question, "When you set out to learn words, where do you begin?"

At, of course! Here, we take our cue from vocabulary education experts, good teachers who know how to introduce their students to words that are not only interesting and challenging, but that are also likely to appear in texts students read as they proceed through school. Teachers chose these words to give students the most bang for their buck. 

At, we seek out these bang-giving words as well. We trawl newspapers, the Internet, and contemporary and classic literature looking not just for which words appear, but for how often. From these words, we create a pool to teach on the site. Then, as you play the Challenge, we use the technology behind it to create a customized subset of that pool just for you. These are words that you don't know, but are likely to see again and again out in the world.

So next time you look at the list of words you're learning, don't compare it to the unknowably large English lexicon. Think of it rather as a map, the words points in the constellations that give shape to an unknowably-large number of stars.