6.作补足语
有宾语补足语和主语补足语两种。
1)作宾语补足语

有一些及物动词除跟宾语外，还需要有一个成分作逻辑上的补充说明，使得宾语的状态或行为或特征等的意思完整。这个成分称为补足语。由于说明宾语，因此称宾语补足语。不定式可作宾语补足语。如：
Many parents allow their children to make their own decisions.
许多家长允许他们的孩子自己拿主意。
(allow – permit 允许)
The trainer made the elephant dance before audience.
训兽中使大象在观众前跳舞。
注：
① 通常要求带to不定式作宾语补足语的动词有：advise, allow, ask, cause, consider, expect, find, imagine, know, tell, think, want, wish等www.ＥxamdＡ.CＯM
(advise – persuade 劝说 )
(think – suppose 想 )
② 要求不带“to”的不定式作宾语补足语的动词(一般为表示“感觉”或“使役”的动词)有：feel, have, hear, let, make, notice, see, watch, listen to, look at
③ help后面的作宾语补足语的不定式带“to”或不带“to”都可以。
help Mary wash her clothes
help Mary to wash her clothes
2)作主语补足语
带有宾语补足语的谓语动词变为被动语态时，宾语成了主语，宾语补足语也就相应地成为主语补足语。当动词不定式用作主语补足语时，一律要用带“to”的形式。如：
Their children are allowed to make their own decisions.
允许他们的孩子自己拿主意。
The elephant was made to dance before audience.

使大象在观众前跳舞。
不定式结构在英语文章中使用频率较高, 如下面的这段文字中(4个句子), 不定式结构出现了5次, 请大家确认这些不定式结构在句子中的语法功能.
(1)So far there is no data to suggest that people living on metal-rich soils experience a potential health hazard. (2) They are also the most likely ones to eat potentially dangerous metal-rich soil. (3) Some trace metals are alleged to cause cancer and also known to cause poisoning中毒. (4) There is a vital need to understand the potential risks and long-term health effects of living on naturally contaminated soils.
提示: 相邻语句往往围绕同一中心发展, 在词语上常常表现为: 相邻语句中出现呼应的词语.
分析：第1，2，4句中不定式是作定语;第3句的不定式是作主补;
(hazard –danger 危险)
(hazardous – dangerous危险的)
(contaminate -- pollute污染)
Ⅲ不定式的逻辑主语
如要表明不定式或不定式的动作发出者(即逻辑主语，就要在不定式前用for+名词(或代词的宾格)。如：
Is the road wide enough for two cars to pass?

这条道路是否宽得足以使两辆车通过?
(wide – broad 宽阔的，辽阔的)
The conference is too important for you to miss.
这会议太重要了，你不能错过。
(conference – meeting 讨论会，协商会;会议)
(important –essential 重要的)