连词连接词、短语、句子，表达并列、转折、原因、结果、条件、让步等逻辑。
13.1 并列连词
and 和
but 但是
or 或者
so 所以
for 因为
yet 然而
nor 也不例句：
I like tea and coffee.
我喜欢茶和咖啡。
He is young but experienced.
他年轻但有经验。
Hurry up, or you will be late.
快点，否则你会迟到。13.2 从属连词
从属连词引导从句。
原因：
because, since, as条件：
if, unless, as long as时间：
when, while, before, after, until, as soon as让步：
although, though, even though目的：
so that, in order that例句：
I stayed at home because it rained.
因为下雨，我待在家里。
If you work hard, you will succeed.
如果你努力，你会成功。
Although he was tired, he kept working.
虽然他很累，但他继续工作。13.3 英语中 because 和 so 通常不同时使用
中文常说“因为……所以……”，但英语中一般不说：
错误：Because it rained, so we stayed at home.正确表达：
Because it rained, we stayed at home.
It rained, so we stayed at home.同理，although 和 but 通常不同时连接同一主从结构：
错误：Although he was tired, but he kept working.
正确：Although he was tired, he kept working.
正确：He was tired, but he kept working.