古人云，“少壮不努力，老大背单词”。各位挣扎在红黄蓝黑各种宝书中的同学或许要问，这单词要背到什么时候才算够？我们不妨来看看外国人的词汇量是多少。

Britain’s Guardian newspaper, in 1986, estimated the size of the average person’s vocabulary as developing from roughly 300 words at two years old, through 5,000 words at five years old, to some 12,000 words at the age of 12.
1986年，英国《卫报》估算英国人2岁的单词量约为300个，5岁时为5000个，到了12岁，词汇量在12000个左右。

The Guardian’s research suggested that it stays at around this number of words for the remainder of most people’s lives—adding that this is roughly the same number of words as those drawn on by a popular newspaper in the course of producing its daily editions—while a graduate might have a vocabulary nearly twice as large (23,000 words). Shakespeare had one of the largest recorded vocabularies of any English writer at around 30,000 words.
《卫报》的研究认为大多数人之后的词汇量都不会有太大的变化。它还指出，12000词汇量基本等同于流行报纸每天文章里的词汇量。但是大学毕业生的词汇量大约是其2倍，约23000个。莎士比亚则是所有英语作家中词汇量最大的之一，高达约30000个单词。

Francis and Kucera (1982) suggest that the 2000 most frequent word families of English make up 79.7% of the individual words in any English text, the 3000 most frequent word families represent 84%, the 4000 most frequent word families make up about 86.7%, and the 5000 most frequent word families cover 88.6%.
Francis和Kucera在1982年发表的研究结果称，2000个最常用单词覆盖了79.7%的英文文本内容，最常用的3000单词及变形的覆盖率达到84%，4000最常用单词及变形的覆盖率为86.7%,当词汇量增加到5000时，覆盖率为88.6%。

综上所述，英语学习者的第一个目标是2000常用单词，这样就能看懂将近80%的英文内容。至于终极目标则是20000单词，也就是和受过良好教育的英国人的词汇量相当（想跟莎士比亚PK的学霸当我没说）。

需要注意的是，认识单词和会用单词是两码事。词汇量达到一定水平后，在对话、写作中使用这些单词的能力对英语水平的影响更大。