3. 复合结构不定式：由for + 名词（或代词宾格）+ 动词不定式即构成复合结构的动词不定式。其中for本身无意义。for后面的名词或代词是不定式的逻辑主语，这种不定式在句中可作主语、表语、宾语、定语或状语，如：It is very important for us to get everything ready for the harvest. 当作表语用的形容词表示不定式的逻辑主语的性质或特征时，就用介词of而不用for引出不定式的逻辑主语，这些形容词一般有good, nice, kind, wise, silly, stupid, foolish, right, wrong, careless, impolite等，如：It is very kind of you to help him every day.
