The way I understand modes is that they are an offset of another scale. The same notes but you make the root note or start the scale in a different position.
You have worked out that the song fits the D scale. A mixolydian is the 5th degree of the D scale D - E - F - G - A (1,2,3,4,5), which makes A the root or home chord. It uses the chords from the key of D, but starts and ends on A …. Here endeth my poor knowledge
When you play the chord progression of Louie Louise, what chord feels like ‘home’ - the one all the other chords seem to move to? For me its definitely A. So the key is A. But what sort of A?
Looking at the other chords, the Em is the one that seems ‘out of place’ diatonically, as E major is the 5 chord in the key of A major. This Em is ‘borrowed’ from the parallel key of Am. Check your circle of fifths and you’ll see its the 5 chord of Am.
So you could say its in A major with a borrowed chord from the parallel key.
You could also look at it by writing out the notes of all the chords in the progression. When you do, you’ll find all the notes of the A major scale, except the 7th note, which, instead of a G#, its a G. So its a b7.
A major scale with a b7 is the mixolydian mode, so A mixolydian.
That is a reasonable first analysis.
Note - were that to be the case, the Em would be denoted as ii (lower case for minor and diminished chords).
However, because the chord A is the resolution chord, the home base, it is the tonic here and needs to inform the analysis.
A major scale, scale degrees and its chords:
1, 2, 3, 4, 5, 6, 7 → A, B, C#, D, E, F#, G# → A, Bm, C#m, D, E, F#m, G#dim
If you know about chord construction and how stacking thirds from the major scale builds the triads you will know where those chords come from and their constituent notes.
A → A, C#, E
Bm → B, D, F#
C#m, C#, E, G#
D → D, F#, A
E → E, G#, B
F#m → F#, A, C#
G#dim → G#, B, F#
What we perform this process in reverse from the given chords of the progression in Louie Louie?
Chords
A → A, C#, E
D → D, F#, A
Em → E, G, B
We can fill chords in three of the seven spaces and due to the Em chord need to change G# for G (the 7th scale degree becomes b7th - shown in bold).
1, 2, 3, 4, 5, 6, b7 ← A, B, C#, D, E, F#, G ← A, --, --, D, Em, --, –
By stacking thirds we could compelte the remaining chords if wanted.
1, 2, 3, 4, 5, 6, b7 ← A, B, C#, D, E, F#, G ← A, Bm, C#dim, D, Em, F#m, G
Where:
Bm → B, D, F# (as above)
C#dim → C#, E, G
F#m → F#, A, C# (as above)
G → G, B, D
The three chords can be seen as coming from a scale that is not A major. They derive from a scale whose root is A but whose 7th scale degree is the note G, a b7. That scale is A mixolydian. The progression is a I, IV, v, IV in A mixolydian.
@sclay also mentions that the Em could be viewed as a borrowed chord. That is also a valid view though in terms of any melodic analysis and any thoughts of playing lead lines over the progression, it too would point towards an emphasis on the b7 note G.
If and when you do work through more theory and have covered Justin’s lessons on modes, the circle of fifths etc you may find useful complementary and supplementary reading here:
That is often how they are taught - “it’s the major scale but starting on a different note”. I think that particular approach to teaching and learning modes does a disservice to being able to understand, hear and use modes for musical creativity. Modes are scales (with unique intervals and chords) in their own right. Hence I wrote such a large topic in seven parts.
I hope that helps.
Cheers
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