1. 两者都可用来修饰不定代词、形容词、副词、动词、介词短语等，此时两者常可换用。如：
Its almost [nearly] impossible. 那几乎是不可能的。
He is almost [nearly] as tall as her. 他差不多与她一样高。
He almost [nearly] always arrives late. 他差不多总是迟到。
He fell and almost [nearly] broke his leg. 他跌了一跤，险些跌断了腿。
Almost [Nearly] all the students passed the exam. 差不多所有的学生都通过了考试。
修饰动词时，通常应放在行为动词之前，特殊动词之后(见上例);修饰形容词、副词、名词等时，通常应将其放在被修饰词语之前，否则会造成错误。如：
他几乎工作了一整天。
正：He worked almost all day.
误：He almost worked all day.
我们当中几乎每一个人都读过这本书。
正：Almost every one of us read the book.
误：Every one of us almost read the book.
2. almost 可用于 any 以及 no, none, nobody, nothing, never 等否定词之前，但 nearly 一般不这样用。如：
Almost any man can do it. 几乎任何人都会做。
Almost no one came to the party. 几乎没有人来参加晚会。
I almost never see her. 我几乎从未见过她。
但是，两者都可用在否定动词之前。如：
He almost [nearly] didnt catch the bus. 他差点没赶上公共汽车。
3. nearly 前可用 very, pretty, not 等词修饰，但 almost 之前不能用这些词。如：
Its not nearly so difficult as you think.这远不像你想`象的那么难。
The car is pretty nearly new. 这汽车几乎是全新的。
注：not nearly 意为远非, very [pretty] nearly 意为几乎，都是习语。
4. 有时 almost 可表示十分相似(但又不完全相同)，此时不用 nearly。如：
I almost wish Id stayed at home. 我真有点后悔没在家里呆着。
Our cat understand everything hes almost human. 我们这只猫什么都懂 快通人性了。