Most people would be shocked to learn that when linguist Hartvig Dahl studied over one million words of conversations, the twenty most commonly used words constituted 37% of the conversations! This points up an important fact about learning vocabulary. If you learn the one thousand or so most commonly used words in a language you should be able to understand about 80% or more of an average conversation or text. But the second thousand most common words will increase your comprehension by only about ten to fifteen percent at most. So it is important to focus on the most commonly-used words and master them first to get the most mileage out of your vocabulary study.