Discussion Groups / English Usage / July 2009

In this sentence "Each one" is implied, therefore the verb agrees with
'one'.

"Each" is an adjective, modifying an elided noun, and has therefore
taken on the role of a noun. Some will say it is a pronoun, in the same
way that "that" and "those", and numerical or demonstrative adjectives
are pronouns.

Don't let it fluster you that many people use "Each" as a plural, as
well as a singular subject.  Plural and singular "they" has been
discussed ad infinitum here, and the world still turns.

 I learned that "each" and "every" _must_ be used as singular, with the
verb following suit, but I wouldn't correct anyone else's (another one!)
usage.
Each and every person has one head, and therefore puts on "his*" hat.
*his, see singular "they/their" in paragraph above.

It is an adjective.  "Each" implies plurality, but considers the members
of that plurality one at a time, and hence is a sort of singular.  
Nonetheless, logic is idiomatically breached when the modifier is placed
immediately after the subject (as in "we each" or "they each") and the
verb then conforms to the number of the grammatical subject, despite the
"one at a time" force of the word.

Thus, in the first sentence--which is elliptical for "Each one has"--the
implied singularity governs the verb, whereas in the second idiom allows
the plural subject to control.

There are several sticky points in the full usage of "each" (for example,
number control reverts to singularity in the first person plural--but not
the third--when the order is reversed, as in "We have each his own
problems").  There is no simple, general rule: the topic must be studied
and learned.

(There is a good discussion at the entry "each, every" in Wilson
Follett's _Modern American Usage_.)