Good question with no simple answer at all. Power chords are neither major nor minor. They do exist at interval spacings apart from one another however. If we look at an example and follow through the various options it gives.
Power Chord progression:
| G5 | C5 | E5 | G5 | A5 | B5 | C5 | D5 | G5 |
All chords are power chords.
If we space them out alphabetically:
A - - B - C - - D - - E - - x - - G - - A
- A → B is a whole tone
- B → C is a semitone
- C → D is a whole tone
- D → E is a whole tone
- G → A is a whole tone
Using Justin’s guidance from the lesson:
We have four instances of two chords a full tone apart. We have one instance of two chords a semitone apart. All possible options are shown in this grid.
Given there are four potential paths to consider if we start with the chords that are a whole tone apart, it makes sense to limit our options. We will work from the B → C chords being a semitone apart and fix those two chords in one of two possible ways. We can them see what results.
First, we will make the B and C chords fixed as the iii minor and the IV major chords. It must necessarily follow that G is I major, A is ii minor, D is V major and E is vi minor. We do not have a vii diminished chord. These chords are shown in blue on the grid.
The power chord progression above would become:
Second, we will make the B and C chords fixed as the vii diminished and the I major chords. It must necessarily follow that D is ii minor, E is iii minor, G is V major and A is vi minor. There is no IV major. These are shown in yellow on the grid.
The power chord progression above would become:
It may now be a simple case of playing these progressions using the full range of chords and listening carefully to see which sounds best.
I hope that helps.
Richard
Foot note:
Many genres that are very power chord centric will have progressions that are non-diatonic and use a range of power chords that are not in the key of the song. Such power chord progressions do then become very tricky to analyse without greater musical context, especially harmonic context such as the vocal melody notes etc. Many lead guitar solos will switch around minor and major pentatonic scales that match the underlying power chord when there is no one obvious key the chords all fit within.