动词不定式是由 to 与一个动词结合而成的，如 to walk，to inflect，to run 等；分裂不定式（split infinitive），顾名思义就是把 to 与这个动词分割开来，通常用副词或副词短语来隔开，如 to boldly go，to casually walk，to gently push 等。1. 动词不定式可以当作名词、形容词或副词使用，例如：
Juan played his guitar to entertain the audience.
Today is a great day to go to the beach.
I only want to talk to you.
We ordered a pizza to share with the family.
The rain ruined my plan to tend the garden.
Juan played his guitar to expertly entertain the audience.
Today is a great day to finally go to the beach.
I only want to quickly talk to you.
We ordered a pizza to generously share with the family.
The rain ruined my plan to carefully tend the garden.
改后的句子看起来没有任何不妥，但是学校里的老师会觉得不对，甚至会纠正这种写法。1. 当修饰语放在不定式短语后面不会造成歧义或改变句子的意思时，就没有理由使用分裂不定式，例如：✔: He urged me to walk up casually and say hello.❌: He urged me to casually walk up and say hello.2. 在有些场合如果使用分裂不定式时，那么就会使句子显得不够精炼，特别是当修饰语太长或太复杂时，例如：
你非得玩得这么大声吗？
分裂不定式：Do you have to so loudly play?
不定式：Do you have to play so loudly?
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1. 若一个语法屡禁不止，那么存在就是合理的。有的时候当分裂不定式中的修饰语比较简单且不会太长时，使用分裂不定式不仅会显得精炼有力，而且可以避免产生歧义，例如：a. I asked her to quietly leave. (✔)b. I asked her quietly to leave. (❌)c. I asked her to leave quietly. (❌)解析：句 a 中的 quietly 可以明确是用来修饰 leave 的，但是句 b 和 c 都会产生歧义，到底是悄悄要她离开，还是要她悄悄离开，也就是 quietly 有可能是修饰 asked，也可能是修饰 leave，从而造成歧义。2. 有些时候必须使用分裂不定式，因为修饰语放在句子的其他任何地方都不合理，例如：
a. They’re expected to gradually come down in price to about $50 to $75 each. (✔)b. They’re gradually expected to come down in price to about $50 to $75 each. (❌)c. They’re expected to come down in price gradually to about $50 to $75 each. (❌)解析：此句中的修饰语 gradually 放在其他地方都显得不合理。We expect to more than double profits this year.Caterpillar plans to more than triple employment at its four-year-old diesel generator plant in Newberry.卡特彼勒计划在纽贝里建立四年的柴油发电机厂增加三倍以上的员工。解析：这两句若不用分裂不定式，那么 more than 将无处安身。
