6)在介词but初中英语语法总结初中英语语法总结，except之后，如果其前有动词do的某种形式，其后不定式一般不带to，反之则必须带to，表示“不得不初中英语语法总结，只能”。例如：1.He will do anything except work on the farm.2.There was nothing left for the enemy to do but surrender.3.The spy was both hungry and cold;there was nothing left for him but to give in.4.I had no choice but to wait till it stopped raining.

　　下面一些短语是固定搭配，不带to：can not help but，can not choose but，can not but，do nothing but，have nothing to do but。例如：I can not but admire his courage.

　　如果上述句中有do，to省略：I did nothing but watch TV last night.

　　如果是下面一个固定搭配，就带to：I have no choice but to give up my idea.

　　7)紧跟在why或why not之后的动词不定式总是不带to。但是，紧跟在who，what，which，whether等连接词后的不定式带to。例如：Why stand up if you can sit down?Why not ask your teacher when you don't understand the meaning?You needn't decide yet whether to study arts or science.

　　4

　　不定式的完成式和进行式

　　1)构成完成式：to+have done进行式：to+be doing

　　2)用法

　　完成式：如果不定式所表示的动作(状态)发生在主要谓语动作之前初中英语语法总结，那么不定式就要用其完成式。

　　进行式：如果主要谓语动作(情况)发生时，不定式所表示的动作正在发生，那么不定式就要用其进行式。例如：1.She feels relaxed to have finished writing her thesis before the deadline.2.The Vikings are believed to have discovered America.3.When you called me last night，I happened to be working on the computer.

　　5

　　不定式的被动形式

　　当不定式的逻辑主语是动作的承受者时，不定式要用被动形式，包括它的一般式和完成式。例如：1.For twelve years，Spanish censorship did not allow Lorca's name to be mentioned and his work to be published.2.The snow was supposed to have been blown off the mountain.

　　6

　　不定式的否定形式

　　否定形式是在不定式的标志to前加not。例如：1.I decided not to ask him again.2.Please remember not to leave the lights on when you are out.