Frequency information plays a central role in learning a language. Nation (1990) showed that
the 4,000–5,000 most frequent words account for up to 95% of a written text, and the 1,000
most frequent words account for 85% of speech. Although Nation’s results were only for
English, they do provide clear evidence that, when employing frequency as a general guide for
vocabulary learning, it is possible to acquire a lexicon that will serve a learner well most of the
time. There are two caveats to bear in mind here. First, counting words is not as straightforward
as it might seem. Gardner (2007) highlights the problems that multiple word meanings, the
presence of multiword items, and grouping words into families or lemmas, pose for counting
and analyzing words. Second, frequency data contained in frequency dictionaries should never
act as the only information source to guide a learner. Frequency information is nonetheless a
very good starting point and one which may produce rapid benefits. It therefore seems rational
to prioritize learning the words that you are likely to hear and read most often. That is the
philosophy behind this series of dictionaries.