I kind of agree with both... 7 notes or 12...

There are 12 semitones, but 7 "names". An "A#", an "A" and an "Ab" are all A's. When spelling chords or scales one uses the correct name.

E.G. a "C" triad is C, E and G. One could spell it C, Fb and G but then, even though it's still the same notes, it is no longer considered a 1, 3, 5 triad, it's a 1, b4, 5 triad...

Seems silly I know, but then consider a diminished 7 chord:
1, b3, b5, bb7
This equates to:
1, b3, b5, 6 but technically that would be a half dim6 chord rather than a full diminshed 7 chord...

Confused yet?

"Correct" spelling is why you will see ## and bb notes in orchestral scores. I've often seen things like an A folowed by a Bbb - keeps the chord spelling right even though it's the same note.

Technically correct, but it doesn't help when playing - sometimes it's just plain confusing until you see the relationship.

Another example: I'm currently in rehearsals for Mary Poppins. there is one point in the score where there is an attaca segue from the end of one song into the next. My part has a series of 3 tied semibreves (whole notes). The first two are Ab's in the last 2 bars of the first song, tied together and also tied to the first note of the second song which is in a different key, and written as a G#.

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