sky vs. skies (long post)

[Billionbridges.com]

A native Chinese speaker on a translation mailing
list posed the following question:

"Why 'the skies' but not 'the sky' in the following
sentence: 'And that's without having to see the rubble
or listen to the fighter jets patrolling the skies?'"

This engendered an interesting discussion among the
native English speakers on the list, especially since
various dictionaries don't seem to give a satisfactory
explanation of the sky/skies problem (ie. it's a problem
for non-native English speakers who can't figure out
when to use which). I thought some of their responses
might be of interest to ADS people, and obtained their
permission to post them here. Any responses would
be much appreciated.

"To my mind there is a time and reference element
involved.  'sky' would imply to me a one-time event or a
timeless event, whereas 'skies' seems to give me the
feeling of separate, discrete episodes the repeat
themselves over a stretch of time."

"Rather than existing as a more literary trope, perhaps
'skies' refers to an earlier conception of 'skyness'--one in
which the sky is not a contiguous plane uniting the world.
Statements like 'fly the friendly skies' and 'The jets are
patrolling the US skies' may refer more to the sky-land
connection.  Fly to new lands with their respective new skies.
That way, the states would be broken up into different regions
--as nations are with their respective air space."

"'The skies over New Jersey are clear.' (weather)
'The sky over New Jersey is clear.' (most likely meaning there
are not planes in the air)"

"'V2s rained from the sky.' (one-time event)
'V2s rained from the skies.' (over a period of time)"

"To me, a native Australian English speaker, if I hear 'the sky',
in the context 'patrol the sky' it takes the meaning ' all of the
sky', whereas 'the skies' means discreet sections of the
[all-inclusive] sky."

[Note: I couldn't bring myself to break up the post below,
so I cut and paste in its entirety]

If I may indulge in some cognitive grammar:

First, but not to belabor the obvious, "sky" is singular and
"skies" is plural.  This is important because these metaphors
involve situating a point in time or space and then either recognizing
placement or movement.  Also none of us are in the sky at the time
we make the statements. (What would "pie in the sky" be from
an airplane?  And would it taste better in first class?)  So here we
might say that we are using sky as a landmark or ground for
locative descriptons.  We might then note that there are at least 2
kinds of locative construal here- figure-ground and trajector.

Figure-ground is used for placement and seems to encompass
singular usage of sky: the pie is in the sky, sky is where the limit is,
so high as to be in the sky (to paraphrase Tony's great list).  In all
these examples there is no movement.

Trajector involves movement, hence we have to break the sky into
pieces so that we may move from one to the other.  Largely these
pieces are conceptual, but may be legal as in the national borders
intimated by United's slogan, or temporal as first noted by Tony.  Note
the action verbs in: patrolling skies, raining V2s, flying skies, gray
skies clearing up (again Tony's list!).

Further consider the use of weather- "The skies of the Midwest
are rarely cloudy." It doesn't denote action, but "rarely" involves
comparison of multiple things (of 100 days of sky, one was cloudy).
Weather is also active as a metaphor, as we say, "His mood changes
like the weather", "mercurial" for temper from the substance's use in
thermometers, and so on.

What about when either sky/skies is acceptable?  "The sky/skies
over Honolulu is/are clear".  Well first of all the singular/plural is
still different.  Also Tony points out that conceptually they are
different.  "V2s from the sky" is not as bad as "V2s from the skies",
because the latter is a longer time period- a time trajectory is
established.  One problem, as a native speaker, is "sky is clear"
and "skies are clear" - Both could be weather for me.  Probably we'll
find that weather is its own idiomatic domain, separate from use of
sky as a place.  Further, as a place for airlines, only singular sky
can be clear over one location.  (Though we might say, "skies the
world over are clear").

So what do these cognitive grammarian prototypes mean for
translation?  As a rough guess at this late hour, I'd say- got an
action verb, object movement, or time change- use "skies".  But
if its a simple locative thing, say prepositional in/at, stick to "sky".

Please bear in mind that this is a *rough* guess.