Intervals are often greater than one Octave, so we'll extend the Major Scale to two (2) Octaves to help us study Intervals.
Intervals over an Octave
As we look at intervals, we'll be using a two octave major scale. We want a two octave major scale because intervals are often greater than one octave. For example, the one octave scale shows scale degrees one through seven. Eight is where the octave starts over. This is fine for intervals of a second to a seven. But intervals go beyond this. It's common to see intervals of 9th 10th 11th 13th and so on.
We can easily add the scale degrees needed for these intervals by extending our major scale one more octave. To make a two octave major scale, we'll pick up where we left off in the one octave scale, and add the same notes one octave higher. For the remaining scale degrees just continue adding numbers like we did before 9, 10, 11, 12, 13, 14, 15.