（1）句子主语和不定式动词可构成逻辑上的主谓关系
这一句型中的形容词通常表示人的性格特征或行为表现。如：
brave　careful　careless　clever　considerate
cruel　foolish　generous　kind　modest
nice　polite　rude　selfish　silly
stupid　thoughtful
例句
a. He was surprised to learn how much he had spent.
b. The boy was careless to break the window.
（2）句子主语和不定式动词可构成逻辑上的动宾关系
a. She is interesting to listen to.
听她讲话很有趣。
＝It is interesting to listen to her.
b. Relativity theory isn’t easy to understand.
= It isn’t easy to understand relativity theory.
c. She is very nice to talk to.
= It is very nice to talk to her.
d. Mary is easy to get on with.
= It is easy to get on with Mary.
e. English is difficult to speak.
f.Football is very interesting to watch.
句子主语与不定式动词为动宾关系时，我们要注意以下三点：
1）不定式一般不用被动式（最容易出错），而多用主动形式表示被动含义：
a. English is difficult to be spoken.*
b. Football is interesting to be watched.*
2）不定式后不能再加宾语：
a. Football is very interesting to watch it.*
b. She is very nice to talk to her.*
3）不定式动词所带的介词不能省略：
a. She is interesting to listen.*
b. She is easy to get on.*