I've seen a handful of common music theory questions around the internet, so I wanted to collect the answers into a single place. Here ya go!
A tritone consists of 3 whole steps, and is found between the 4th and 7th scale degrees of a major scale. For instance if we are in the key of C, our scale degrees are:
F to G is a whole step, G to A is a whole step, and A to B is a whole step, giving you a tritone between F and B.
When going from a major scale to a minor scale, the 1, 2, 4, and 5 scale degrees will always stay the same. The most important degree that always changes is the 3rd, which is lowered by a half step.
So for instance, to get from C major to C minor, you change the 3rd degree of E to Eb. The 6th and 7th scale degree may or may not change depending on whether it is the natural minor, melodic minor, or harmonic minor scale.
Major triads occur on the 1, 4, and 5 scale degrees. Or, in the case of chords, the I, IV, and V. In the key of C, these triads/chords are:
Major triads will occur on the 3, 6, and 7 scale degrees of a natural minor scale.
The natural minor scale has the same notes as it's corresponding major scale. So, if we are in C Major, the natural minor key is A Minor.
Remember from above, the major triads are on C, F, and G. The A natural minor scale is:
So looking at C, F, and G, we can see that they are the 3, 6, and 7 scale degrees.
Minor triads occur on the 2, 3, and 6 scale degrees of a major scale. Or, in the case of chords, the ii, iii, and vi. In the key of C, these triads/chords are:
The typical doo-wop chord progression often uses chords built on the I, IV, V, and vi (or 1, 4, 5, and 6) degrees of the major scale.
For instance, in the key of C, these would be C major, F major, G major, and A minor.
In a major scale, the three scale degrees that are strongest in establishing tonality are:
These three scale degrees, I, IV, and V, play crucial roles in defining the key and creating harmonic movement within a major key.
The degrees of a major scale are:
The notes of a C major scale are as follows: