BBC英语学习:each和every的不同用法--By Roger Woodham

Each and every are both determiners used with singular nouns to indicate quantity. Each indicates two or more objects or people and every indicates three or more. Each can also be used as a pronoun, but every cannot be. Study the following:

each ~ both

each ~ individual; every ~ all

We tend to use each if we are thinking about members of a group individually, and every if we are thinking of them in total. Compare the following:

every NOT each

With adverbs - almost, nearly, practically, etc, we have to use every to emphasise that we are talking about the group as a whole:

We have to use every to refer to repeated regular events, as in once every, twice every, etc. Study the following:

 

each NOT every

Remember only each can be used as a pronoun, irrespective of whether we are describing two or more of something or three or more of something. Study the following:

If we want to use every in a similar way, indicating three or more of something, we must insert one before of them as every has no pronominal form itself. A lot of word stress is put on one so that in effect it means every single one of them. We can use each one of them in a similar way. Study the following and the earlier examples of this structure: