What a fine coincidence! Earlier today I learned something new about each other
, and here you've asked a question to which my new knowledge applies.
But first, the instances of each other
in your second and third examples are reciprocal pronouns
. The two words go together as one reciprocal-pronoun unit. I believe that's why you feel them to be as one. I, too, feel them to be as one, though I have never, if memory serves, seen each other
spelled as one word in high-quality published writing.Each other
is not a reciprocal pronoun in your first example. There needs to be a slight pause between each
; otherwise each other
would be understood to apply to they
rather than to block
, which I assume you are using as a noun (blocks of wood, blocks of a town, etc.).
As to why each other
in the second and third sentences are spelled as two words, I learned today that, historically, the preposition in such constructions was placed between the two words. The following passage is from Otto Jespersen's The Philosophy of Grammar
(1924), which I ordered earlier this week and started reading today:
"The distinction between a formula and a free combination also affects word-order. One example may suffice : so long as some+thing is a free combination of two elements felt as such, another adjective may be inserted in the usual way : some good thing. But as soon as something has become a fixed formula, it is inseparable, and the adjective has to follow : something good. Compare also the difference between the old ' They turned each to other ' and the modern ' they turned to each other '".
-- Jespersen, Otto. The Philosophy of Grammar. Henry Holt and Company: New York, 1924.
Historically, then, your second example might have read as follows. I'm not sure whether a comma would have been added or not:
- They looked each at (the) other.
- They looked, each at (the) other.
Perhaps each other
, in its reciprocal pronoun usage, is on its way to being spelled as a single word. If so, I would imagine that text-messaging culture is assisting in that development.