When to play what

Minor keys are a bit more complicated, because there are three different minor scales.

The chords that occur in a particular key come from harmonizing the scale - here's the C scale harmonized:

G A B C D E F
E F G A B C D
C D E F G A B

chord: C Dm Em F G Am Bº


The natural minor key uses the same notes as the major key, so A natural minor will harmonize to the same chords, but in a different order:

E F G A B C D
C D E F G A B
A B C D E F G

chord: Am Bº C Dm Em F G


The harmonic minor key raises the seventh scale degree - in A minor, all the G notes will be sharped. That changes the chords:

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

chord: Am Bº C+ Dm E F G#º


Then there's the melodic minor scale - going up, this has the sixth and seventh degrees sharped; going down it's the same as the natural minor scale:

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

chord: Am Bm C+ D E Fº G#º


Other types of scales are harmonized in the same way, by building chords based on every third note of the scale.

If you're playing in the relative minor, it's the sixth note of the major scale.

So, for example, you listed the C scale progression:

C Dm Em F G Am Bdim C

The sixth note is the beginning of the relative minor, hence in the key of Am, the progression is:

Am Bdim C Dm Em F G Am

Hope that helps.

once you know the structure of chords you can do any scale, like now, i will make up a scale randomly

B C# D E F# G A Bb B

take first note (B) third one (D) fifth one (f#)... first chord is B minor
take second note (C#) then fourth (E) and sixth (G).. second is C# dim

wow.. weird.. i just wrote out B harmonic minor, i thought it was one note different but change Bb to A#... ok, ill WORK out a new scale

C D# E F# G# A Bb C

C-E-G# = C augmented
D# F# A = D# diminished
E G# Bb = havent got a clue
F# A C = F# diminished
G# Bb D# = dont know

etc, but have it working in right numbers of spaces inbetween the notes.

It'd be pretty tough to invent a new scale. I think they've all been done.

"They're not really rules, more like guidelines..."

If you only played strictly in the key, you'd never play the flat-7 in a blues song...

For example, Moondance is written in Am, but the F# is prominent (Bm and D), so it's sorta like being written in G.

And there are lots of songs where the VII is not really proper. D-C-G is considered to be in D, but could be said to be in G.

And what key is Brown Sugar in? C Eb Ab Bb G

There are real "theory" explanations for why these chords and notes work for a given song, but sometimes they get a bit esoteric for me. My favorite: "The V of V allows a C# in the key of G" for Brown Eyed Girl.

Huh? :?

-Laz

"They're not really rules, more like guidelines..."

If you only played strictly in the key, you'd never play the flat-7 in a blues song...

Hi, Laz. Blues does not follow the rules of Western harmony. It just doesn't. It uses dom7th chords on the I and IV sometimes and throws in lots of "blue" notes into what is essentially major key harmony, i.e. the b3, b5 and b7. These "out of key" notes, borrowed from the parallel minor, are what characterises blues.

That said, blues does follow the primary rule of chord substitution, that 2 chords can sub for each other if they share 2 or more notes. Thus the I7 (1-3-5-7) can sub for the I (1-3-5).
For example, Moondance is written in Am, but the F# is prominent (Bm and D), so it's sorta like being written in G.

A Dorian actually. Again, the 2 note shared rule allows you to sub a Bm for the Bdim and D for the Dm.

Note an interesting fact about all these songs that "break the rules":

They almost always use an easier to finger chord in place of the diatonic chord.

I can't remember how many songs in F I've seen with a G instead of Gm, songs in C with a Bm instead of a Bdim, songs in Am with a D instead of Dm and so on. Almost always the easier chord.
And there are lots of songs where the VII is not really proper. D-C-G is considered to be in D, but could be said to be in G.

D-C-G would usually be in G. However, hang around long enough on the D and you can make it sound as if D is the home chord. This is known as D mixolydian and is pretty common in rock and folk and such.

The bVII is very often added to what are basically major key songs in rock and pop, giving a slightly edgier, less happy feel.
And what key is Brown Sugar in? C Eb Ab Bb G

On the face of it, C minor. It would feel relentlessly sad and bleak with a Cm I chord, so you reduce the minor feel by substituting a Imaj for the I minor.

There are real "theory" explanations for why these chords and notes work for a given song, but sometimes they get a bit esoteric for me. My favorite: "The V of V allows a C# in the key of G" for Brown Eyed Girl.

The V of V is not a complex concept. The V is the most important chord in the key, along with the I. Every chord sounds good with its V. If you're playing in G, the V is D. A major (A-C#-E) sounds good with D. That's where the C# comes from.

Finally, of course, any note can be used as a passing note.

The blues scale works over major or minor key accompaniments with the same root note.

The "major blues scale" or "traditional blues scale," related to the major pentatonic as the blues scale is to the minor pentatonic, only works over a major key backing. That's also what you get if you use the blues scale of the relative minor (as I think has already been mentioned above) of the major key accompaniment. It's a modal thing. You hear this in lots of New Orleans music, Southern gospel and such. A quick way to experiment with this on guitar is to just move any blues scale patterns you've been playing up three frets toward the nut. Only works if you're playing over accompaniment; by itself it'll still sound just like the same solo line, just transposed a step and a half lower. Makes a lot cheerier, major-sounding effect than the blues scale.

Blues does not follow the rules of Western harmony. It just doesn't.

Blues is, apparently, deeply rooted in African tribal music. Now, if someone could shed some light on the scales that they use(d) .........

Blues is African-American music. It surely draws on African tribal traditions, but there's no African music that we'd recognize as blues. It was developed in America by African immigrants or their descendants using a combination of African and European styles, with mainly European-based instruments adapted to playing (as nearly as they could) what they were singing. But it's vocal music first. If you listen to blues singers (and slide or string-bending guitarists), they often use microtonal stuff that doesn't neatly fit on a fixed-pitch instrument like a piano. Particularly what's been called "the blues third," in between the minor third and the major third. There have been many volumes written about "the African roots of blues," and a few hours spent searching keywords on Google and reading the results will be time well spent if you're interested in the topic. Taj Mahal has put out some CDs of modern traditional music from Mali, and has brought musicians from Mali over here and jammed with them, blending their music and American blues traditions. Interesting stuff. Unfortunately, outside of Mali many of the native musical traditions in Africa have been suppressed and lost completely, and we're left to speculate about what they were like.

A quick way to experiment with this on guitar is to just move any blues scale patterns you've been playing up three frets toward the nut. Only works if you're playing over accompaniment; by itself it'll still sound just like the same solo line, just transposed a step and a half lower. Makes a lot cheerier, major-sounding effect than the blues scale.

I'm just starting on solos over backing tracks, so I'm trying to sort this all out. I've been using a simple A-D-E backing track. Please let me know if I'm getting this:

1) If I play the A blues scale, or the A minor pentatonic over this I'll get a bluesy sound.

2) If I move three frets toward the nut, I'll be playing the F# blues scale (or eliminate the "blue" note, and it's the F# minor pentatonic), and I will get a cheerier sound).

3) The big question - are these the "correct" scales to play over this progression under these circumstances? In other words, do I know what I'm talking about?

Thanks in advance for your help.

Yep, you've got it :)

Right! :D

Thanks y'all for the help.

But my last question still stands, what about all of the other "common" scales? Say Harmonic minor. Does it work out that same way as was described previously?

I thought I'd answered that one above:
The harmonic minor key raises the seventh scale degree - in A minor, all the G notes will be sharped. That changes the chords:
Code:

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

chord: Am Bº C+ Dm E F G#º

There are only two sets of scales where you can move down three frets and be in the relative scale: the major/natural minor, and the major/minor pentatonic. So if you're trying to find A harmonic minor, you have to locate the A root and go from there.

There aren't really shortcuts to the other scales - you just have to learn the scales and the chords that harmonize from them.