too...to是个常用句型结构,一般表示否定意义。例如:My sister is too young to go to school. 该句型和enough to结构意义相反,例如上句可以改为: My sister is old enough to go to school.
　　有时在too...to结构中再加上一个否定词,表示肯定意义。可以加在too前,也可以加在to前。例如:
　　John is never too disappointed to want a try. 约翰决不失望,还想再试一试。
　　This English gramma book is not too difficult for us to understand.这本语法书并不太难,我们看得懂。
　　He was too angry not to say it. 他太生气了,难免要说出这种话来。
　　She is too careful not to have noticed it. 她那么仔细,不会不注意到这一点的。
　　下面再举一个例子,看该怎么翻译:They seem to be too nervous and were too anxious to leave. 应译为:他们看来过分紧张不安,并且过分急于离开。如果译为“急于不离开”,显然是前后矛盾的。说明too...to结构并非只能表示否定意义,也可以表示肯定意思,这取决于too后面的表语形容词。在be too anxious to do, be too eager to do, be too willing to do, be too easy to do等结构中,均应表示肯定意思。例如:
　　I’m too pleased to meet you. 见到你很高兴。
　　He’s too willing to accept the task. 他乐意接受这项任务。
　　so as to有“以便、使得”的意思,用来引导目的状语,相当于in order to,只不过口气稍弱,并且不能放在句首。例如:
　　He got up early so as to catch the first bus.
　　She spoke slowly so as to be heard by everyone.
　　so as to也可以表示结果,例如:He struck the snake so as to break its back.他对蛇一击,结果打断了它的背脊。在多数情况下表示结果都出现于so...as to的结构中。对比经过改动后的前面两个例句:
　　He got up so early as to catch the first bus.
　　She spoke so slowly as to be heard by everyone.