Thought: Major Sevenths - The Chords That Defined The Sound Of The 70s?

Every decade is known for a unique sound, characterized by the stylistic choices made by many popular artists in that era. The 60s had psychedelia, the 80s synthesizers, the 90s grunge, and so on. That is, every decade except the 70s.  What's different about the 70s? Well, they did spawn several distinct movements in rock music - metal, progressive rock, and punk to name a few. The musical diversity of the 70s probably makes it hard to pin a specific sound to them. Yet,for the longest time I couldn't stop thinking about what defines 70s music. After all, most of my favorite songs are from that decade.

My theory? The 70s sound so good because they're responsible for bringing to life one of the beautiful chords in all of music - the Major 7th chord. Here's an example of the chord in use by French composer Eric Satie:

Gymnopedie No. 1/Eric Satie

I soon realized that many of my favorite songs from the 70s have this chord somewhere, whether in the verse, chorus, or a bridge or outro. In some of these songs, no instrument may even actually be playing a maj7. However, when combined with the other instruments and the vocals, the overall effect is that of a maj7 chord. I've tried to list my top ones below (there are many more that I can't recall just now).

It's Too Late/Carole King
Make It With You/Bread
I Know What I Like/Genesis
Rain Song/Led Zeppelin
How Deep Is Your Love/Bee Gees
Year Of The Cat/Al Stewart
Color My World/Chicago
We've Only Just Begun/Carpenters
Beast Of Burden/Rolling Stones
Dreams/Fleetwood Mac
Bennie And The Jets/Elton John

So that's my take on what makes the 70s sound so unique. The maj7 is just one of those sweet sounding chords that lends a melodious, laid-back feel to so many songs of that decade. No wonder that so many of the top '70s artists used it, whatever the genre.