This question already has an answer here:
The white keys are taken in the order of 1-3-5-6-8-10-12 notes from the 12 note chromatic scale. Why only those selective 7 notes and not other sets and why only 7 notes?
Why not the 1-4-5-6-8-9-10 set of seven notes as each of those notes are in consonance with the root note?
Note: I am quite convinced why there are 12 notes in the octave based on the inclusion of perfect fifth but I am curious about the inclusion of other six notes, especially the dissonant ones like major second and major seventh excluding the consonant minor third and minor sixth.
So basically I have two questions.
- Why those seven notes?
- Why only seven notes?
Edit: The staff notation itself is built on the basis of the pattern of those seven notes.
The interval F-B is called as Augmented Fourth (B is the fourth white key starting from F) and the interval B-F is called as Diminished Fifth ( F is the fifth white key starting from B) when they both have exactly 6 semitones of intervals in between.