In a previous question I asked whether you can use maj7 chords in place of a dominant chord within a key, and the answer was no – these chords contain different notes. That makes sense to me, however if you look at a blues progression, it will be something like I7-IV7-V7, where all of the chords are dominant!
So, does that mean the inverse is true – that while you can’t use maj7 instead of dom7 in a key, you can use dom7 instead of a maj7? Or is this some kind of special allowance made for the blues style?
Thank you!
The main thing with dominant chords is they change the sound entirely. Generally speaking, we can group all dominant chords together, i.e., 7ths, 9ths, etc. All minor chords together – min, min7, min9 etc and all major chords – Maj, Maj7, Maj9 etc. They don’t necessarily sound the same but they have common attributes.
Major chords have 3 and 7
Minor chords have b3 and b7
Dominant have 3 and b7
These notes give each chord group a similar character which makes them more likely to be interchangeable, but not definite, just more likely. It’s perfectly OK to go against the grain as long as you think it sounds OK.
Blues doesn’t really get a special allowance, although I guess you could look at it that way if you wanted to. Music theory isn’t strict, it’s just a guide. Someone, at some time thought it sounded good to take a blues progression and make every chord dominant, they liked it – we got used to hearing it, so it no longer sounds wrong (if ever it did).
The whole blues sound is based on a bit of a clash of tones. We don’t worry about theory, we just do what others do. That is, we can take a I-IV-V using major chords and play a minor (pentatonic) scale over the top. The major and minor third clash but we like it.
We can make them all 7ths, use the same scale and we still like the sound. All is OK.
We could of course use major scales as well over the I-IV-V. It creates a different sound but works just fine. Make the chords all dominant and we can still use major scales, only we might be more selective with the way we use the scale. With major blues we’re not expecting to hear so many clashing notes so we might make it more riff and lick based and take more notice of chord tones.
Make the chords all minor and suddenly the major scale doesn’t work so well. There’s probably no reason for this other than nobody really does it so we’ve never got used to liking it.
Take all of the above and give it to a jazz player and they might do something entirely different that sounds nothing like the blues we expect to hear. This is why it’s important to realise that music theory is very much style dependant. All it does is gives us a grounding or a kind of template to work from and helps us all speak the same language.
It’s all quite complex if you want to theorise everything. Sometimes it just doesn’t really matter, we just learn and practice what various styles do and don’t worry too much that it contradicts the general theory.
This can turn into quite a complicated discussion, where many musicians will potentially disagree. The hard part of all this is telling somebody that they should learn theory and then just ignore it. All I can say is keep learning and one day things should start to make some kind of sense.
