Accidental in Beethoven's Piano Sonata No. 8 - Adagio cantabile

[bryan52803]

Hello, I'm learning to play the song listed in the title. I have the sheet music from Alfred Publishing Co., Inc and it says EDITED BY ARTUR SCHNABEL on the cover.

I'm new to piano and I have a question about an accidental at the start of the second staff. The base note of the chord on the lower staff shows a flat accidental symbol in front of a D quarter note. However, this note is already flat relative to the natural note because it's written in Ab major (Ab,Bb,C,Db,Eb,F,G,Ab). Now my understanding was that accidentals do not apply to octaves nor do they persist past a measure. There is a D natural in the staff above this, but it is 2 octaves up and in another measure.

So what's going on here? What note am I to play? Thank you in advance.

Bryan

[stevebob]

Now my understanding was that accidentals do not apply to octaves nor do they persist past a measure.

Your understanding is correct ... technically.

In practice, though, it is very common for "courtesy accidentals" or "cautionary accidentals" to be printed anyway just as a reminder.  Usually such usage is limited to the immediately following measure, but some hypervigilant editors might be even more aggressive (as in the example you mention).

https://en.wikipedia.org/wiki/Accidental_%28music%29#Courtesy_accidentals