If在英语句中的位置和三种类型

Question

If在英语句中的位置和三种类型

Answer 1

1. if 引导名词从句,作主语、宾语：
It is not certain if / whether he will go abroad.
（置于句首时,只能用whether: Whether he will go abroad is not certain.)
I wonder if he knows it.
(介词后只能用whether: We are talking about whether we will go.)
2. if 引导条件状语从句, 该从句可置于主句前后:
If he goes, I won't go. = I won't go if he goes.
If I were a bird, I could fly in the sky.
3. if only用于感叹句:
If only I could fly. = I wish I could fly.
4. 用于if...or not:
I don't know if he will go or not.
= I don't know whether he will go or not.
= I don't know whether or not he will go.
5. 用于if so、if not:
If so, I will go. If not, I won't go.
6. 用于as if、even if:
He looks as if he knows it.
Even if he knows, he won't tell me.