- （认为正确） praise; justify:
praise the past to condemn the present;
是古非今
justify his action
是其所为
- （表示两种事物同一，或后者说明前者）:
He is a language professor in Dalian University.
他是大连大学的语言教授。
English, Dutch and German are cognate languages.
英语、荷兰语、德语是同语族的语言。
- （联系两种事物，表示陈述的对象属于“是”后面所说的情况）:
It was winter outdoors, but spring indoors.
院子里是冬天，屋子里是春天。
- （与“的” 字相应，有分类的作用）:
That house is built of stone.
那所房子是石头造的。
I came to see her.
我是来看她的。
- （表示存在）:
sweating all over;
满身是汗
There is a verdant lawn in front of the dormitory.
宿舍前是绿茵茵的草坪。
- （表示让步，含有“虽然”的意思）:
It is a good poem all right, but it's a bit too long.
诗是好诗，就是长了点。
I'm certainly going, but I'll be a little bit late.
我去是去，可是得晚一点儿。
- （“是”前后用相同的名词或动词，连用两个这样的格式，表示所说的几桩事物互不相干，互不混淆）:
A friend is a friend; a foe is a foe; one must be clearly distinguished from the other.
敌是敌，友是友，必须分清界限。
- （用在名词前，含有“适合”的意思）:
The tools are not put in the right place.
工具放的不是地方。
This rain has come at just the right time.
这场雨下的是时候。
- （用于问句）:
Is your sister a doctor or a nurse?
你妹妹是医生还是护士?
You're tired, aren't you?
你是累了不是?
- （用在句首，加重语气）:
Who told you?
是谁告诉你的?
It was he who first came to reason.
是他第一个明白过来。
