动词不定式的基本形式是“to + 动词原形”，有时可以不带to。动词不定式(或不定式短语)没有人称和数的变化，在句子中不能作谓语。动词不定式仍可保留动词的特点，即可以有自己的宾语和状语。动词不定式同它的宾语或状语构成不定式短语。如：to read the newspaper, to speak at the meeting 等
动词不定式具有名词、形容词和副词的特征，因此在句子中可以作主语、表语、宾语、宾语补足语、定语和状语：
作宾语 She wants to borrow my radio.
作状语 He came to give uw a talk yesterday.
作宾语补足语 She saked me to speak more loudly.
作定语 I had something to eat this morning.
作主语 To learn a foreign language is not easy.
注：作主语用的动词不定式常常为it替代，动词不定式(或短语)放在后面。例如：
It is not easy to learn a foreign language.
It took us three days to do the work.
动词不定式的否定形式由“not+动词不定式”构成. 如:
Tell him not to be late.
The policeman told the boys not to play in the street.