Why is the interval between some notes varied such as with b sharp and c flat?

Answer 1

It does seem odd that you might want to refer to B sharp sometimes, or to sometimes call a pitch G sharp and call the same pitch A flat in another piece. These differences have to do with formal harmony, and are important technical differences. Scales in standard western harmony are made up of successively named notes, as in C D E F G A and B. Those names are not repeated in a scale, and none are omitted. In the scale of E major, the notes are named in this way, although some are sharped in order to maintain the structure of the diatonic major scale. E F G A B C D and back to E. You can determine which are sharp. Now consider the scale of E flat. The notes will follow the same order, or course: E F G A B C D and back to E. In E major, the third note will be G sharp; it follows F and precedes A. But in E flat, the fourth note will be A flat. It cannot be called G sharp, because the note before the A flat is G natural.