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.