动词不定式是一种非谓语动词形式，其结构为“to+动词原形”，其中to是其符号，它没有人称和数的变化。动词不定式在句子中可以用作主语、表语、宾语、补足语、定语、状语等。以下是一些使用动词不定式的例子：
作主语
To be a doctor is hard.
To learn English well is not easy.
To say is to believe.
作表语
Her goal is to become a famous singer.
The purpose of the trip is to relax and have fun.
作宾语
I like to read books.
She decided to travel around the world.
作补足语
I saw him go out.
They found the door open.
作定语
The take-off was smooth.
A walk in the park is refreshing.
作状语
I came to help you.
She left early to catch the train.
单独使用
To be or not to be.
Have you ever tried skydiving？
建议
明确句子结构：在使用动词不定式时，首先要确定句子的主要成分，以确保不定式在句子中扮演正确的语法角色。
注意逻辑主语：有些动词后面跟不定式时，需要考虑逻辑主语是否可行，例如，当动词表示“使”、“让”时，逻辑主语通常是人。
避免句子过长：虽然动词不定式可以表达复杂的思想，但过长的句子可能会影响清晰度，尽量保持句子简洁明了。
通过以上例子和建议，你可以更好地理解何时使用动词不定式，并在实际应用中更有效地运用它。