Seventh chords: "maj7" vs. just "7"

Hi folks,

When I first encountered the “Fmaj7” chord in Justin’s beginner lessons, I was a bit confused about why it has “maj” in there but other major mode chords just say “7”, like “D7”, “A7”, etc. But I never heard about “F7”, and nor did I ever hear about “Dmaj7”. So my question was, is “Fmaj7” just another way to say “F7”, or are they different chords?

Well I found out the answer, but it wasn’t obvious to me, and it took some digging to figure it out, so I’m posting an explanation in case there are other beginners out there who are as confused by this as I used to be. Maybe I can save somebody some frustration.

7 = Dominant Seventh

If you see a “7” immediately after a note name, like “C7”, “D7” or “A7”, that is shorthand for a dominant seventh chord. This chord is made up of the major triad, plus the minor seventh. The notes are 0, 4, 7 and 10 semitones up from the root note. So in a C7 chord, the major triad is C, E, G and the minor seventh is a B♭.

You might be thinking “hang on, B♭ isn’t even in the C major scale”, and you would be correct. That’s just how a dominant seventh chord works. It uses a note that is not normally part of the scale. Why is it called a “dominant” seventh"? It’s some obscure musical theory stuff that I don’t quite understand yet. Don’t worry about that right now.

You might have also noticed that the open C7 chord on guitar has C, E and B♭, but doesn’t actually have a G. What’s up with that? Well it turns out, the perfect fifth (the G in this example) is not very important in a dominant seventh, so you can just leave it out and the chord still counts as a dominant seventh, due to reasons that are once again pretty obscure. Don’t worry about that right now either.

maj7 = major seventh

If you see “maj7” after a note name, that means it’s a major seventh chord, which is much less popular than the dominant seventh. This chord is made up of the major triad, plus the major seventh. The notes are 0, 4, 7 and 11 semitones up from the root note. So a Cmaj7 would be C, E, G and B. In a major seventh, all the notes are in the major scale.

m7 = minor seventh

If you see “m7” after a note name, that means it’s a minor seventh chord, which is the minor triad plus the minor seventh. The notes are 0, 3, 7 and 10 semitones up from the root note. So a Em7 would be E, G, B and D. In a minor seventh, all the notes are in the minor scale.

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