begin 和 start 后面可以跟动词不定式，也可以跟 -ing 形式，意思通常没有明显区别。

    She began playing / to play the guitar when she was six. 她六岁开始弹吉他。

    He started talking / to talk about golf, but everybody went out of the room.

    他开始谈论打高尔夫球，但大家都溜出了房间。

在 begin 和 start 的进行式之后，要用动词不定式。

    I'm beginning to learn karate. 我刚开始学空手道。

    (不能说：I'm beginning  learning karate. )

understand, realise 和 know 出现在 begin 和 start 后面时，要用不定式形式。

    I slowly began to understand how she felt. 我慢慢开始明白她的感受。

    (不能说：... began understanding...)

    He started to realise that if you wanted to eat you had to work. 他开始认识到

    要吃饭就得工作。 (不能说：...started realising ...) 

   （以上摘自《牛津英语用法指南》第四版 105.10）