（1）不定式时态、语态的构成
不定式的时态、语态是不定式作为动词的特征体现。英文中把动作分为四种不同的完成程度：一般动作、进行动作、完成动作和完成进行动作。同理，不定式也具备这四种形式。不定式同样还有语态方面的变化。现列表如下：

 
（2）不定式的一般式（to do）
不定式的一般形式to do所表示的动作通常：
1）与主要谓语所表示的动作或状态同时或几乎同时发生。
a.I am glad to see you.
b.I heard him sing last night.（此句型中要省略不定式的标志to，但是被动语态中不能省略：He was heard to sing last night.）
2）或是在主要谓语动作之后发生。
We plan to go to the sea this summer.
（3）不定式的完成式（to have done）（四、六级考试重点）
不定式的完成式可表示：
1）发生在谓语之前的动作
由上述第（2）点得知，不定式的一般式不能表示发生在谓语之前的动作，若要表示不定式的动作比谓语动作先发生，则不定式要用其完成式to have done。
a.We are happy to have visited so many historic places in Beijing.
在北京参观了那么多名胜古迹，我们感到很开心。
b.Humans are believed to have evolved from the primate species.
人们相信，人类是由灵长类动物进化过来的。
c.Albert Einstein, the great American scientist, is estimated to have had the incredible intelligence quotient of 200.
据估计，美国伟大的科学家爱因斯坦的智商高达200，这真让人难以置信。
d.The rain seems to have stopped . It means the rain seems now to have stopped a few minutes ago.
e.I am very sorry to have bothered you with so many questions on such an occasion.
f.I am sorry not to have come on Thursday. (=I am sorry that I didn't come on Thursday.)
g.The redwood appears_________some 100 years ago in northern forests around the world.
A. having to flourish
B. to flourish
C. to have flourished
D. have flourished
正确答案：C。
分析：句子谓语appears表示现在，而some 100 years ago表明不定式动作发生在过去，所以选C。
2）表示“非真实”的过去
用在表示打算、需要、计划等动词过去时的后面，表示过去本打算做但事实上没有实现的动作。这些动词有mean，intend，think，plan，hope，wish，propose等。
a.I meant to have telephoned , but I forgot.
我本来打算打电话的，但是我忘记了。
b.I planned to have visited you last night, but I was too busy.
我昨晚本来想去看你，但太忙了。
我们还可用下边两种结构表达同一种意思：
① was/were to have done, would like to have done, should like to have done
a.I was to have telephoned , but I forgot.
b.I was to have visited you last night, but I was too busy.
② 过去完成时+ to do
用上述动词的过去完成时态来表示此意，但此时不定式不能用完成式，而要用一般式to do。
a.I had intended to see you, but I was busy.
不说：
I had intended to have seen you, but I was busy.*
b.He was to_________to a foreign university but the war prevented.
A. have gone
B. go
C. be going
D. have been going
正确答案：A。
因此，表示“过去想做而实际未做成”的事，有下述三种表达方式：
① was/were to have done, would like to have done, should like to have done
② intended (meant, designed, hoped, planned, thought, wished, proposed) + to have done
③ had intended (meant, designed, hoped, planned, thought, wished, proposed) + to do
3）偶尔表示“将来”
She hopes to have finished the work by the time he comes back.
她希望在他回来之前把这些工作都做完。
这句话本来是由宾语从句转换而来的：
She hopes that she will have finished the work by the time he comes back.
由于句中by the time对应的主句一般与完成时态连用，因此将宾语从句改成不定式需要用不定式的完成式，这时，表示的是一个将来完成的动作。
（4）不定式的进行式（to be doing）（不常用）
不定式的进行式可表示：
1）正在进行的动作
通常用在appear，happen，pretend，seem等动词之后。如同进行时态那样，动词不定式的进行式（to be doing）用于表示在我们谈论的时间（现在或过去）正在进行的动作，或者说与谓语动作同时发生的动作。
a.He pretended to be listening attentively when the teacher came by. 当老师走过时，他假装正在专心听讲。
此句相当于：He pretended that he was listening attentively...
b.He pretended to be sleeping when she came in.
c.He happened to be singing in the room when I came in this morning.
2）反复发生的一般性动作
因为进行时态可以表示一个最近一段时间内持续的一般性动作，同样，不定式进行式可表示一种反复发生的一般性动作，此时带有很强的感情色彩。
a.In the 1980s and early 1990s, athletes entering international sports competitions seemed to be getting younger and younger. Talented young athletes...boys and girls...were spotted early on in their school career, and were given special training.
b.I'd rather read than watch television; the programs seem _____all the time.
A. to get worse
B. to be getting worse
C. to have got worse
D. getting worse
正确答案：B。
（5）不定式的完成进行式（to have been doing）（较少用到）
表示在谓语动作之前已经开始并且一直在持续进行的某一动作。
a.They are said to have been collecting folk songs in Yunnan.
= It is said that they have been collecting folk songs in Yunnan.
据说他们一直在云南收集民歌。
b.He seems to have been sitting there all day.
c.I seem to have been learning English for over ten years.
d.The little girl seems to have been watching TV all this evening.