I ask this question - because it's something my daughter came across in her theory and wasn't sure of the answer. I would have said instinctively that it was a G natural but have recently had pieces of music in which the accidental was relevant to all notes of the same name across about 3 octaves - (Kloze exercises.) And can't entirely remember what I have been taught on the subject.

Tricky one, I would say, especially without seeing the bar concerned in context with what follows.

I've seen music have additional accidentals, sometimes in brackets, in order to make this kind of thing clear - ie a natural sign on the other octave G in order to specify it's not the same as the G# in the lower octave, or a # sign on both Gs if they are both meant to be sharp. I haven't got my theory reference books handy to look and see if there is anything stated for this case. In short, I don't know either!

The pink book says:
"Unlike the sharps and flats in a key signaure, an accidental applies only to the line or space on which it is written" (page 14).
It then gives an example in F major where a second natural sign has to be added to a Bb up an octave.

Depends on the period of the music. Accidentals are not always repeated at the octave in baroque and classical music because you can generally tell by the context which note is meant. That is no longer the case after the beginning of the nineteenth century as the music becomes more chromatic.

I found an actual example of this in, believe it or not, one of the cadenzas to Mozart's Andante in C this week. I automatically played a descending scale passage with an F natural, despite the presence of an F# accidental in a lower octave earlier in the bar, and was pulled up by my pupil who thought I should have played an F#. She took a lot of convincing that my version was correct - but in the context of the phrase I knew that it should be an F natural.

At the level of theory your daughter will be doing it would be a G natural.

Also on the style guide of the publisher. The AB book does tend to lay down 'facts' which are merely one way of doing things.

I'd say it meant someone had been either careless (if it was meant to be a sharp) or iscourteous (if it was a natural)

Remembering something smebody wrote on a notation forum, who had been on a notation course in an American university, and their lecturer had asked them how long after they put an accidental should they need to put in a natural (or sharp or flat if cancelling the accidental back to the key-signature). Most of them said just until the bar-line. His answer was that while it was technically so, many orchestral players reckoned anything up to four bars depending opn the music.

It certainly makes sense to make it quite clear that you haven't just forgotten. Like if you have a bar of semiquavers, all F#s, that's just one # at the beginning of 16 Fs, and the next bar you have 16 semiquavers which are all F naturals. Would you think "oh, there's beena bar-line, it will be obvious that these aren't also sharps" or would you put a natural? (perhaps in brackets)?

I think a G at the top and as G# at the bottom does lead you to wonder if someone had forgotten something. A natural at the top would be courteous.

Love it! And in anticipation of anyone complaining about weird modern music, think about how much can happen in a couple of seconds and four bars of a Haydn quartet scherzo.

In real music there is no definite answer. Apart from the fact that different periods, different composers, and different publishers had different ideas about it, sometimes composers were careless and simply forgot to indicate the sharp.

However in an AB theory exam, the "answer" is that it would be G natural.

To avoid any uncertainty a considerate composer would mark the note with either a natural or sharp sign.

I remember having this problem with a piece of music which I did for my G6 (a modern edition of a baroque piece). There was a B-on-the-middle-line made flat, and later on in the bar a B-above-the-stave. I'd played this piece for ages without realising that I'd played both Bs flat. I actually noticed this in a lesson one day, and said to my teacher "Oh, hang on, should that second B be flat or not?" He then played the phrase through with the flat, and then with the natural. It was definitely meant to be flat, the natural just sounded awful...

My teacher said many baroque composers would fail their G5 theory if they were to take it today writing as they did in their day

We then got in to further discussion, as this piece was titled as 'in d-minor' but the key signature contained no flats (or sharps!) If you are in a minor flat key, the 'last flat' on the key signature is the sixth note of the scale - so it would often be sharpened (as in your melodic minor ascending scale). So it was quite common in the baroque era to just leave that last flat out of the key signature (in minor flat keys), and instead just pop in the accidental flats when you didn't want it to be the sharpened-sixth-back-to-natural.

Of course, then we go on to facsimiles created before the natural sign was invented, where the sharp sign means 'raise a semitone' and the flat sign means 'lower a semitone', rather than distinctly meaning the sharp or flat note name So in a piece with Bb in the key signature, a # before a B would mean a B natural, not a B sharp. Most of the time

At least for AB theory exams, the AB theory books are explicit about what they mean - so you can give a definitive answer in those cases

When was it invented? I've always thought the natural was such a wonderful shape tht it might possibly have been designed like that even today if it had been the result of a committee of professional designers. Look at it next to a flat, and lt looks like a sharp with a few bits knocked off; put it beside a sharp and it looks decidedly flatty. So it does do this "sharpen this flat note" or "flatten this sharp note" very cleverly.

I'm in no way an expert but my understanding is that it developed from the three hexachord system - the 'Natural' (C,D,E,F,G,A), the 'Molle' (F,G,A,Bb,C,D) and the 'Durum' (G,A,B,C,D,E).

The Molle hexachord required a Bb in order to maintain the same sequence of tones and semitones as in the Natural hexachord. The 'b' that was used was a round-headed 'b' resulting ultimately in the flat key signature. The Durum hexachord required a B natural and in Mediaeval times this was shown with a square B. The square B was cumbersome to draw, requiring four pen movements. Instead composers drew it as an 'h' - requiring only two pen movements. B natural thus became known as 'h' and is still called that today in German-speaking countries.

I'm sure someone will correct me but that has been my understanding.

I remember you mentioning this in another thread a while ago, when the same question cropped up. I knew I'd recently encountered a situation where I left out some accidentals because they were in a different octave, but realised that it sounded badly wrong. Sure enough - it was Dido's Lament. It only shows F# in the treble and not in the bass. I had to write them in, in the end, because I kept on leaving them out..

I should probably have said 'widely used' rather than 'invented' Certainly the facsimilies I've used of Handel, Marcello, Schickhardt don't seem to go in for natural signs (but then I don't think they bother cancelling accidentals - because they just let the bar line take care of it, and you don't get 'courtesy naturals' in those days...)

The "flat" was required to avoid the tritone so it was described as "molle" (soft?") as opposed to "dur" (hard?). The flat symbol was a minuscule "b" and the natural as noted was a "square" B.

Sorry, I forgot to add the 'soft' and 'hard' hexachord descriptions.

Thankyou all for your replies and the quote from the pink book.

I was interested in the answer but also the wider theory - i certainly got that. Thankyou