Have you ever wondered what people mean when they say things like “flat 3, flat 5 and flat 7?”
When people use these terms, they’re referring to a note by it’s scale degree number.
The scale degree formula for a major scale from the root note to the next octave of the root note, regardless of the key, is – 1, 2, 3, 4, 5, 6, 7, 1.
Some people count the octave of the root note as an 8, but I’ve come from the school that refers to it as a 1.
The scale degree formula for a natural minor scale from the root note to the next octave of the root note, regardless of the key, is – 1, 2, flat 3, 4, 5, flat 6, flat 7, 1.
The reason why we refer to the 3rd, 6th and 7th scale degrees of this scale as flat, is because they’ve been flattened (moved down the fretboard a semi tone) in relation to the 3rd, 6th and 7th scale degrees we play in the major scale.
All theory is taught in relation to the major scale.
If you’re reciting the scale degrees of a different scale, flat and sharp scale degrees let people know HOW it’s different from the major scale.
Or, better still – HOW the major scale has been ALTERED in order to MAKE the new scale.
Something that can make this easier to grasp is to think of every other scale besides the major scale as a MUTATION of the major scale.