不定式，如as to watch, to throw, 和to see是动词最基本的形式。不定式能做名词、形容词和副词。

　　Noun(作名词): I love TO SWIM. To swim是动词love的宾语。

　　Adjective(作形容词): The person TO MEET is here. To meet 修饰名词person。

　　Adverb(作副词): Sue paused TO EAT lunch. To eat修饰动词paused，表示目的。

　　上面第三个句子，不定式表示目的：why she paused or for what。这个句子也可以写成：Sue paused in order to eat lunch.

　　in order to不wordy，尽管有同学认为这个短语相对于to来说wordy。无论是否用短语in order to，要注意它们表示目的的作用。看下面这个例子：

　　Right: The contractors DEMOLISHED the building to keep it from falling down accidentally.

　　动词demolished的主语是名词contractors，同时contractors也是不定式to keep的隐式主语(implied subject)，动词不定式to keep在这里表示demolished的目的，keep的宾语代词it的先行词是building。

　　Wrong: The building WAS DEMOLISHED to avoid falling down accidentally.

　　在这个例句中动词was demolished的主语是building，同时building也是不定式to avoid的隐式主语，但是a building自己不能avoid something intentionally。所以上面的例句是无意义的(nonsensical)。

　　再看下面这个例句

　　Right: The building WAS DEMOLISHED to keep it from falling down accidentally.

　　这个例句的主语是building，同时building也是不定式to keep的隐式主语，但是代词it是不定式to keep的宾语，指代building。由于building是不定式to keep的宾语，所以上面的写法也是正确的，表示的意思是the same unnamed people who demolished the building wanted to keep it from falling down accidentally.

　　注意，不定式虽然能做动词，但是不是名词结构。所以，虽然不定式能够做主语，但是一般来说，GMAT语法用代词it来指代主语，放在句首。

　　动名词(gerunds)-ing作名词，与不定式相比，动名词更像名词结构，所以动名词既能做动词的宾语，又能做动词的主语，还能做介词的宾语。如以下例句：

　　Subject of verb(作动词的主语):SWIMMING is fun. Swimming是is的主语。

　　Object of verb(作动词的宾语): I love SWIMMING. Swimming是love的宾语。.

　　Object of preposition(作介词的宾语): I dream of SWIMMING. Swimming是介词的宾语。

　　我们学过，动名词分为一般动名词和复杂动名词，动名词前面有冠词的是复杂动名词。看以下例句

　　Simple gerund: EATING apples quickly (more verb-like，更像动词)

　　Complex gerund: The quick EATING of apples (more noun-like，更像名词)

　　记住，一般动名词与复杂动名词不能平行，同时当相应的动作名词存在时不要用复杂动名词，即the quick consumption of apples(动作名词)比thequick eating of apples(复杂动名词)好。

　　如果名词是动名词所表示动作的行使者，那么这个名词必须是所有格的形式，如以下例句

　　Wrong: Mike SWIMMING is the product of new coaching techniques.

　　Right: Mike's SWIMMING is the product of new coaching techniques.

　　在用以上规则时，要检查下，动名词是否是名词?还是名词的修饰词，有时两种用法都说得通，如以下例句

　　Suspect: I like Mike SWIMMING. (=名词修饰语 I like Mike only as he swims, not as he runs? 当Mike游泳时，我喜欢他?OR 名词I like for him to be swimming rather than lifting weights?我喜欢Mike去游泳)

　　可以改成以下句子来避免歧义

　　Right: I like Mike's SWIMMING. (名词= I like his swimming itself.)

　　Right: Mike SWIMMING is a sight to behold. (名词修饰语Mike himself can be the sight.)

　　Right: Mike's SWIMMING is a sight to behold. (The swimming can be the sight.)