动词不定式和动名词都可以用作主语。在意义上相近。但动名词多用来表示泛指或抽象动作，不定式多用来表示特指或具体动作。
例句：谈论那件事没有用/好/浪费时间。
It is no use/good/a waste of time talking about that.
It is no use/good/a waste of time to talk about that.
1.在疑问句中，通常用动名词的复合结构，而不用不定式的复合结构作主语
例句：你的话对他有什么意义吗？
Does your saying that mean anything to him?
Does for you to say that mean anything to him?
2.在“There be”句型中，只能用动名词，而不能用不定式作主语
例句：不知道会发生什么。
There is no telling what will happen.
It is impossible to tell what will happen.
3.当句子中的主语和表语都是非限定动词时，要遵循前后一致的原则，主语和表语在形式上要求统一
例句：眼见为实。
Seeing is believing.
To see is believing.
