He has a knife with which to defend himself.

Question

请问上面的with which是什么用法？请仔细讲解一下。

Answer 1

“介词+which”后接不定式短语作后置定语，相当于一个定语从句。

He has a knife with which to defend himself.

他有一把自卫的刀。

同类例句：

Allow me half an hour in which to wash the clothes.

留给我半小时洗衣服。

He had no pretext on which to break his promise.

他没有违背诺言的借口。

She has saved another thousand dollars with which to support her family.

她又存了1000美元用以接济家庭。

Answer 2

“介词+关系代词”后接不定式短语作后置定语，相当于一个定语从句。
He has a knife with which to defend himself. = He has a knife with which he can defend himself

Answer 3

这是一个定语从句
先行词是knife
所以引导词用Which或that
但介词后不能用that

固定用法 defend with用……防卫
这里把with提到引导词前追答

句子意思是 他有一把用来防卫的刀。

Answer 4

with是介词 which 介词宾语