前此说过了“定冠词的常见用法”，意犹未尽。本文就来谈谈不定冠词（indefinite articles） a/an 的用法。
不定冠词最基本的用途就是用来表示“一”这概念，如：
① A stitch in time saves nine.
② Jason is an internationally known scholar.
此外，a/an 还有下列 6 种用途：
㈠常和time、measurement等有关的名词连用，以表示“每—” 的概念，如：
③ I teach five days a week.
④ This type of vegetables is sold at one dollar a kilo.
⑤ My car usually runs sixty kilometres an hour.
㈡常和 hundred, thousand, dozen 以及数目及数量连用，如：
⑥ That factory turns out at least a hundred tyres a day.
⑦ Noel s monthly salary is a thousand dollars.
⑧ I have a number of sponsored students.
⑨ Mary has a lot of money.
㈢在“of / at”后面出现，以表示“同一类”这概念，如：
⑩ Birds of a feather flock together.
11. Please come one at a time.
12. Things of a kind come together, so do people of a mind.
㈣常在“rather, quite, many, half, what, such”等字后面出现，形成固定用法，如：
13. Tom is rather a fool.
14. I think Chinese is quite a useful language.
15. Many a student has asked that question.
16. The visitor left half an hour ago.
17. What a fine day it is!
18. How can you say such a thing?
㈤用在“so, as, too, how 形容词”这些结构里，如：
19. We have not had so hot a day before.
20. Susan is as clever a girl as Anna.
21. That is too difficult a book for beginners.
22. No one knew how serious a problem it was until later.
㈥出现在许多惯用语中，如：
23. Bob always has a bone to pick with others.
24. Some students turned a deaf ear to the teacher s advice.
25. All must learn a language with an eye to mastering it.
26. I hope you will make an effort to attend the meeting punctually.
27. Jason has an aversion to being idle.
28. The news of Jack s sudden resignation came as a bolt from the blue.