The use of All, Both and Each

In addition to being used as attributive adjectives and as pronouns followed by of, the words all, both and each can also be used in apposition. A word used in apposition immediately follows the subject of a verb, or the object of a verb or preposition, and refers to the same thing as the subject or object. In the following examples, the words in apposition are printed in bold type.
e.g. We both wondered what would happen next.
The boys all looked forward to seeing the circus.
I sent them each an invitation.

In the first two examples, both and all are used in apposition to the subjects we and the boys. In the third example, each is used in apposition to the object them.

Words used in apposition can be referred to as appositives. Like relative clauses, appositives can be defining or non-defining. Non-defining appositives must be preceded and followed by commas.

e.g. Our leader, Tom Smith, was prepared for any emergency.
In this example Tom Smith is a non-defining appositive, in apposition to our leader.

Defining appositives such as all, both and each are not preceded and followed by commas.

e.g. We each have our own ideas.
In this example, the defining appositive each is in apposition to we. It should be noted that although each is singular, the verb have must be plural to agree with the subject we.

When used in clauses with auxiliary verbs or with the Simple Present or Simple Past of the verb to be, all, both and each generally follow the first auxiliary or the verb to be, rather than being used in apposition to the subject of the verb.

e.g. The boys had all been looking forward to seeing the circus.
We are both very happy to see you.
In the first example, all follows the first auxiliary had. In the second example, both follows the Simple Present of the verb to be.