Scope of natural accidental inside a bar

Question

I have a question about natural accidental and its scope inside a bar. As far as I know, all accitentals should last until end of the bar and they affect all following notes on the same line in this bar, unless they're canceled by another following accidental.

However, the following score is a bit confusing to me:

If the natural sign lasts until end of the bar, then the accidental at the note number 2 shouldn't be necessary. And if it would affect only immidiately following note, then accidental at the note number 6 wouldn't be necessary.

Is the the accidental at number 2 just redundant - only for clarity reasons?

Answer 1

It's a mistake.

It might be argued that the second B in the upper stave warranted its own accidental, being in a different voice to the previous one. But it's definitely not a B♭, so there's no possible excuse for the natural at 2.

(That 3/2 fingering in the RH is odd. Almost as if it WAS a B♭ and the 'no thumb on a black note' rule was being rigidly enforced. But I really don't see that as a musical possibility, in this style. (What IS the piece?)

Answer 2

I would argue that the natural at 2 is necessary because of the flat at 6. If I were to come across this score, I would immediately see the similarity between these measures and wonder why some have a B♮ at the end and one has a B♭. The current notation prevents that possible confusion. In my view, no accidental is needed at 4, because the performer will repeat what they just played.

In other words, it's a courtesy accidental, albeit one on a higher level of politeness. But perhaps the engraver could have put the natural in parentheses just to prevent the confusion in this question.

Answer 3

I would read the natural at 2 as a courtesy accidental even though it should really have brackets around it. There isn't one at 4 because that would be overkill. At 6 the flat is definitely necessary, otherwise it would be read as a natural.