So, why does a minor pentatonic work over a major blues?

My musical theory is limited, but I’m guessing it’s something to do with dominant sevenths.

Because music theory and blues are not friends.

I could fancy that answer up a bit, and a proper theory expert could fancy it up a lot, but that's the long and the short of it. If you play blues, throw your theory out the window and just play what sounds and feels right.

(PS: and forget any sort of pentatonic scale - you can happily play most (but not all!) of the notes on the fretboard in a blues context.) 

Tannin said:

Because music theory and blues are not friends.

I could fancy that answer up a bit, and a proper theory expert could fancy it up a lot, but that's the long and the short of it. If you play blues, throw your theory out the window and just play what sounds and feels right.

(PS: and forget any sort of pentatonic scale - you can happily play most (but not all!) of the notes on the fretboard in a blues context.) 

Basically this. 

Blues is a westernafication of African music which doesn't fit into the western classical music analysis framework properly. 

You will notice for example that when playing the minor third you will probably find yourself bending it slightly sharp to get a mictronal blues third and the same is true of the flat five 

More information here:
https://en.wikipedia.org/wiki/Blue_note

Firstly it doesn't really work  ... if the 1 chord is a major and you hit the flat 3rd over it then it grinds melodically ... that's one of my pet hates is people playing in minor pent over a major key .... if you need to stick to a minor pent shape then play the relative minor .... so F#m pentatonic for A

However in any song in any key you only need to worry about playing over the chord as a passing moment. That's where the melodic phrases come from, hitting the choice 3rds. 5ths and 7th's of the underlying chord as you play over it. 

Take something as simple as Apache (showing my age here I know) It starts with an Am but the 2nd chord is a Dmaj .. so you wouldn't stay in strict Am as that has a natural F and the Dmaj has major third of F#  ....So you always bend the key you are playing to these non diatonic borrowed chords. 

I always say when teaching that if you want to play melodically over any song then first make sure you know all the chords of the song and what the additional qualities are ... such as maj7, add 9 etc 

If you analyse it, you've got some pretty cool notes there. 1,b3,4,5,b7. 1 and 5 are chord tones over the dominant 7th chord as is the b7 and the b7 isn't in major pentatonic so minor pentatonic has an advantage there.
The 4 is a little offensive but fine as you don't linger on it. But it's that b3 that really has the attitude. You need to bend it a 1/4 tone to make it really work and it gives that blues flavour. When you look at it like that, it's perfect. (Plus you can add in the b5 for more sassy flavour)

I'm not a blues guy per se, so I only heard about this approach on Eric Clapton's "Change The World" -  which isn't even a blues song lol.  But he does exactly this in a short passage in his solo and I thought it sounded cool.  So I tried it and found when done over too many bars, it sounds awful.  So when I use it, it's over just 1 or 2 counts just to add a blues twist or tension to something.  Others above have explained the theory already.  For me it gives that tension but you'd naturally slide/bend to a common note again (root, 4th, 5th) to resolve.             

LionAquaLooper said:

...  Others above have explained the theory already.  For me it gives that tension but you'd naturally slide/bend to a common note again (root, 4th, 5th) to resolve.             

Guthrie Trapp posted a video yesterday which shows how, in a 1 4 5 blues, the 7th chord is only a semitone away from the next chord you want to play. https://youtu.be/jR39xP-6IyQ

Going back to @HAL9000’s question: It was a revelation to me in my early teens when I realised that the sound I was looking for was the minor scale played over major chords, or to be precise 7th chords. It’s the simplest form of “outside” playing. There is both tension and release in being able to bend or slide between the minor and Mixolydian scales. 

Totally agree with Tannin. Anyone who understands pentatonics won’t be able to play the Blues. 

Theory can still explain the what and the why of the blues though - what it is and why it works. Theory is just explanation. So if it’s explainable, that’s music theory. You probably don’t need words like “chromatic tetrachord”, but theory will give you concepts such as tension and release, flat 7 chords, walking bass, and so on. 

Let's use A Natural Minor (Aeolian)for ease of understanding.

1 2 b3 4 5 b6 b7

This is A B C D E F G 

Minor pentatonic is a reduced version of this consisting of 1 b3 4 5 b7

A C E D G

A Major is 1 2 3 4 5 6 7 only three notes difference to A Natural Minor.

A Major Pentatonic is 1 2 3 5 6

Now if your using Dominant chords which in a I IV V would be

A7 D7 and E7 consisting of

A, C#, E, G
D, F#, A, C
E, G#, B, D

So we have C#, F# and G# which are Major 3rd, Major 6th and Major 7th all of which are the required notes for A Major.

So you can use either Major or Minor pentatonic scales over this progression as well as Mixolydian or perhaps Dorian, I like to use a mixture of Dorian and Blues scale when descending then add some mixolydian notes on the ascent which could be seen as a melodic minor inflection.

You could even change the scale per the chord rather than be static so for instance use A Mixolydian, D Mixolydian and E Mixolydian.

If you wanted to really jazz things up you could substitute the V chord for A# and use the altered scale or whole tone scale.

Point being you can almost justify anything with theory but the real point being does it sound good?

Learn your intervals, learn your scales, learn to construct chords, learn everything you can and absorb as much as possible then forget it all and just play.

I really wish I could understand this like you guys.

jesone said:

I really wish I could understand this like you guys.

It works for some, not so for others. I'm the type of person who'd rather not know too much theory. It tends to push out other stuff in my brain like wedding anniversaries, kids birthdays etc =) 

reposting this

Just keep blues and 7th based tunes in a different box of theory from everything else!

I don't think it does work on a major blues iff you hang about on it but us guitarists have got really good at manipulating it and making it fit

DavidR said:

Totally agree with Tannin. Anyone who understands pentatonics won’t be able to play the Blues. 

Seriously though, Blues is little more than a chord progression, an attitude and a hard life. Put all that together and you have magic. 

This made me chuckle. (And of course, made me give you the automatic wiz anyone can earn simply by agreeing with me.)

Why the chuckle? Because I don't understand pentatonics and I am unable* to play the blues! 

Oh, I can play the proper notes readily enough, I just don't have the feel of it in my bones. I play a lot of blues-influenced songs, but they never sound like blues, they end up being more like swing or rock or country or even bluegrass. I can sit down and watch one of David Hamburger's excellent fingerstyle blues lessons, learn a few great blues licks, go away and practice them for 10 minutes .... and now I'm not playing blues. They have morphed into something completely different. This happens every single time. 

As for understanding pentatonics, I don't. Not even a little bit. I have never understood what the point of leaving out perfectly good notes is. OK, taken to extremes, that attitude would result in everyone playing the 12-tone scale (which would sound like nothing with any shape or form worth listening to) but take the same notion (i.e., that you leave some notes out of the scale to give the other notes shape and create music with a feel and form) too far the other way and you end up with an over-simplified scale that quickly gets very repetitive and boring. After 50 years of playing I have never yet sat down with a guitar and learned a pentatonic scale, and I daresay I never will. What would be the point? Off the top of my head I can't even remember which notes you have to leave out to make one. 

* Exception: I can play blues if someone else is leading. I could accompany you, @DavidR, and do a reasonable job of it on either rhythm guitar or bass because then I'm in a different mindspace, simply trying to make the singer.or lead player sound good, you are controlling the pacing and the feel - but if I'm setting the pace and you are accompanying me ... the result might be music, and it might even be good music, but it certainly won't be blues. 

BillDL said:

Pentatonic scales are simply skeleton scales that work over a greater range of underlying chords than a full major or minor scale would.  What notes you choose to add back in ...

That'd the best simple summary I've seen. 

BillDL said:

Pentatonic scales are simply skeleton scales that work over a greater range of underlying chords than a full major or minor scale would.  What notes you choose to add back in and where to add them to flavour the scale is where knowing the chord and scale theory is useful.  It's not essential because most people would eventually find additional notes that worked for certain things, but knowing some of the theory can speed up that discovery process and allow you to explore things you may not have thought about doing.

All this tosh about "good blues players don't need to or shouldn't know theory" is silly nonsense, as is the notion that before you can authentically play the blues you need to have been stabbed by a jealous husband down at the railroad track after your woman left you and you lost your job and possessions resulting in you having to busk barefoot in the snow while drinking cheap liquor from an old soup can.  Yes "blues" needs a particular "feeling", but there are so many different styles of blues-based music that you don't need to sell your soul to the devil or go and live down in the swamp to be able to play bluesy music.

And I sold my mansion for this rat infested shack thinking it was a bargain!

At great risk I'm going to give you some of my thoughts on this.

@JimmyH started it off well although I would take it in a different direction.

So A minor pentatonic has got

A   C  D  E  G
1  b3  4  5  b7

Then the I, IV, V are
A7 D7 and E7 consisting of

A, C#, E, G
D, F#, A, C
E, G#, B, D

So let's see what happens when you hit any note in A minor pentatonic:

A - it's in A7 and D7, but not in E7; however A is the tonic/key of the whole progression so it's okay.

C - it's in D7, but not in A7 or E7; however if you think of playing in position 1 of Am pentatonic your first finger falls on that 3rd string (C) and pulls it slightly sharp in a very satisfying way. In fact, it's so common it's a crucial (cliche) part of the blues style.

D - it's in D7 and E7, but not A7; However, think about that cliche 2 tone bend up from the 7th fret on the g string, goes straight to E (which is in the A chord).

E - it's in A7 and E7, but not D7; Don't know about you, but this only gets played in passing or deliberately during the V turnaround.

G - It's in A7, but not in the others. In position 1, string 2 it gets bent up 2 tones to A all the time. On string 4 it tends to be ghost note just before hammering onto the A.

I think that all of this means that you generally have a 2 out of 3 chance of landing on a chord tone. On top of that you get used to knowing what sounds good where. And finally, if you do land on a bum note a good one is always only one scale step away so it's easy to fix.

I have also just thought about that SRV trill on the major 9th that he does all the time (especially on the V chord) is basically just hitting the 5th of the V7 chord. 

Major and minor. Up and down the rollercoaster. I gave you seven children. And now you wanna give 'em back!

How often do blues musicians fully state the chords? It might be convenient to notate a typical 12-bar as containing A, D and E for example, but it seems to me that in a lot of cases it's only the root and fifth that are actually played, with the major third perhaps used as an occasional passing note in the bass.

Let's look at this from a different direction (these thoughts prompted by @Stuckfast's post above). What are the notes that you most likely want to play  in a blues or blues-like context? Let's list them from first-choice down to last choice (i.e., the note you are least likely to want to play over (say) a 1 chord or a 5 chord. (The first few are pretty much equal priority, it drops away from there.)

1: tonic
2: b7
3: 5th

After that, the thirds, but you are almost as likely to play a minor as a major 3rd, so:

4: 3rd
5: minor 3rd

Then the non-chord tones which are nevertheless part of the key (insofar as blues has a key

6: 2nd (9th)
7: 6th

Now we get to the fun bits:

8: flat 5
9: b6 (aka b13, aka minor 6th, aka #5)
10 b2 (b9)

And the leftovers -

11: 4th - probably the least "bluesy" note, other than -
12: maj7 - almost never used

You almost certainly won't want to use all of them in a single passage or even in a single song, and I find it's usually best to make a selection - for example, one or other of the two 3rds, with the other no more than a passing note. (Lots and lots of blues/blue-rock used the minor 3rd - think anything in mixo - with the major 3rd as a passing note but is clearly major just the same.) Then the 2nd, b5, and maybe b13. Other notes as desired, but that selection gives a certain feel and makes the core of a song.

(NB: I play solo so this is the stuff I do to make my fingerpicked chords interesting. Flat 13, for example, mostly on the 5 chord when I want to resolve to a minor 1 chord ('coz that works so well!) - note that blues-flavoured stuff morphs between minor and major all the time. I see no reason it wouldn't work just as well for electric lead so long as your bass player and #2 guitarist or keyboard player are on board with it.)

TLDR: make a selection of about 7 or 8 notes that will make up the main feel of your song. Vary at will, but mostly stick to those 7 or 8. 

Despite asking the original question, for blues I’m far more likely to use major pentatonics or the BB box than to use minor pentatonics. To my ears minor pentatonics aren’t really the sound of blues; they’re the sound of blues-rock (and possibly also rock without the ‘blues-‘ prefix).

That's exactly what I was saying earlier about pentatonic scales (major or minor) being a "skeleton" scale upon which you then add other notes to flavour the melody / solo so that it sounds like you want it to over whatever chords are being played underneath it.  Your choice of notes can swing the sound between major or minor depending on what chords you are playing over.

BillDL said:

...  Your choice of notes can swing the sound between major or minor depending on what chords you are playing over…

… and they can include partial bends which don’t exist in any of the major and minor scales.

Tannin said:

11: 4th - probably the least "bluesy" note,

Agreed. However it turns up often enough. Examples are the guitar riffs in Howlin’ Wolf’s ‘I Ain’t Superstitious’ and Little Walter’s ‘My Babe’. Might be the least bluesy note but certainly not out of bounds.

it works bc it's got 3 chord tones of the dominant chord (flat 7) and the sharp nine (minor 3rd) which is usually bent up a half tone and becomes resonant, i.e. a chord tone major 3rd. 
bending the minor third  is a a common, 'merican thang to do when playing the pentatonic, major or minor
Easy way to create tension and release. 
if you don't bend the 3rd it will sound "ok" bc it's got the other notes, but a bit shite at the same time so when you play the minor penta from the route of the maj chord, you kinda have to micro-bend the minor 3rd. 

This, tastefully combined with the minor penta of the relative minor, creates some nice blues lickage..