When do sharps/flats reset?

[briffra]

My acquired understanding on the "stickiness" of an explicit sharp/flat is that it applies for the rest of the bar (i.e. only up to the next vertical line encountered). Also, that it doesn't automatically apply to an octave up/down. So a sharp on middle C does not imply that all other C's above or below should also be sharped for the rest of the bar.

But then sometimes I see explicitly added sharps/flats/naturals which seem unnecessary given this rule, and it makes me question whether my understanding of the rule is correct. For example, notice the first G-sharp in the right hand in here:

http://www.chopinonline.ac.uk/ocve/browse/barview?workid=6352&pageimageid=64780&barid=55

It seems unnecessary to have that sharp notated, given the key signature. But as you can see all the editions add that sharp explicitly in, as if it would otherwise be played natural.

Am I missing something here? Is my understanding of the rule correct?

[dogperson]

Your understanding is correct regarding the nature of accidentals.  In subsequent measures you will sometimes find a sharp or flat unnecessarily added , even though it is self-evident from the key signature. These are called ‘courtesy accidentals’  since they are merely a reminder. Occasionally you will find them in parenthesis.

I personally find it irritating; a wake up call, with the assumption the musician must be asleep and has forgotten the key signature.

[briffra]

haha that's a fun name, "courtesy accidentals".

I can't find an example, but I also feel like there are some exceptions to the rule sometime, where an explicit accidental is omitted for an octave up/down, but it sounds weird if you don't play it, so it seems to be implied. So in the example I gave with the middle C, in some cases it's actually expected/implied that the subsequent Cs (octave up/down) should also have the accidental applied to them. Am I wrong on this, or does this actually happen?

Another small question: suppose middle C is sharped, in treble-clef (e.g. right hand) and in the same bar, the left hand in bass-clef later has to play the same middle C. I assume it should still retain the accidental in such cases?

[dogperson]

If an accidental is omitted from a different octave position on the staff, it is not an exception to the rule but an editorial error.  The rule has no exceptions.

It doesn’t matter which hand plays the note; the only criteria is the position on the staff.

[keypeg]

If an accidental is omitted from a different octave position on the staff, it is not an exception to the rule but an editorial error.  The rule has no exceptions.

Not quite.  Music has evolved historically, and conventions took time to establish themselves.  There was a convention at some (earlier) time, in some particular places, where the accidental was deemed to apply to all notes regardless of the octave - in later times however this was abandoned in favour of what we know now, because of the obvious problems with such a policy.    It's something I remember discussing with my first teacher near the beginning of working on theory.   I was surprised. Those old editions (from where?) don't seem to appear often.

[lelle]

haha that's a fun name, "courtesy accidentals".

I can't find an example, but I also feel like there are some exceptions to the rule sometime, where an explicit accidental is omitted for an octave up/down, but it sounds weird if you don't play it, so it seems to be implied. So in the example I gave with the middle C, in some cases it's actually expected/implied that the subsequent Cs (octave up/down) should also have the accidental applied to them. Am I wrong on this, or does this actually happen?

Another small question: suppose middle C is sharped, in treble-clef (e.g. right hand) and in the same bar, the left hand in bass-clef later has to play the same middle C. I assume it should still retain the accidental in such cases?

In modern editions, accidentals are never implied to apply to a different octave than the one they were written in front of. Can you look for/try to remember an example? I'm quite curious where you have seen this.

[timothy42b]

In modern editions, accidentals are never implied to apply to a different octave than the one they were written in front of. Can you look for/try to remember an example? I'm quite curious where you have seen this.

I can't give you an exact piece but I do run into this in ensemble music and in etude collections.  I would say most of the time the modern rule is followed but it's also fairly common to see it ignored.  I suspect this may occur because notation programs are so popular and inexperienced people write music, rather than being driven by the historical period of the music.  In other words i think it's just a mistake. 

Hmm.  I just tested Noteworthy Composer, the notation program I use.  I wrote two measures of quarter notes in octaves and added accidentals to one octave only, and played it back.  The accidentals applied to both octaves.  So apparently this is a choice within some notation programs.  I don't know what Finale does.