than
/ðæn, ðən, ðn/conjunction & preposition
1
- introducing the second element in a comparison用于比较级的第二个比项之前比：
as prep. he was much smaller than his son他比他儿子瘦小多了
as conjunction Jack doesn't know any more than I do.杰克知道的不比我多。
2
- used in expressions introducing an exception or contrast除…（外）; 与其…（宁愿）：
as prep. he claims not to own anything other than his home他声称除了住房之外, 他一无所有。
as conjunction they observe rather than act.他们观察却不行动。
3
- conjunction used in expressions indicating one thing happening immediately after another表示时间衔接顺序就：
scarcely was the work completed than it was abandoned.
作业刚一完成就被丢到一边了。
USAGE
Traditional grammar holds that personal pronouns following than should be in the subjective rather than the objective case: he is smaller than she rather than he is smaller than her. This is based on an analysis of than by which than is a conjunction and the personal pronoun （'she'） is standing in for a full clause: he is smaller than she is. However, it is arguable that than in this context is not a conjunction but a preposition, similar grammatically to words like with, between, or for. In this case the personal pronoun is objective: he is smaller than her is standard in just the same way as, for example, I work with her is standard （not I work with she）. Whatever the grammatical analysis, the evidence confirms that sentences like he is smaller than she are uncommon in modern English and only ever found in formal contexts. Uses such as he is smaller than her, on the other hand, are almost universally accepted. For more explanation see usage at PERSONAL PRONOUN and BETWEEN.
词源
Old English than（ne）， thon（ne）， thænne, originally the same word as THEN.