OK, this is a little confusing so hang in there.
All chords IN THEORY are built by stacking of thirds (play on a keyboard 1, 3, 5, 7, 9, 11, 13 of any scale and let them sound together.... really, a chord is just a scale spelled out with every other note). We can build a chord on each degree of any scale, so we can build a chord on the 1st, 2nd, 3rd, 4th, 5th, 6th and 7th degree of any minor scale. OK? Still with me???
NOW, in practice we choose the notes we like, and stack them so that they A) sound good and B) are playable.
This is called voicing your chords. We will spend most of this course working on simple, playable and historically useful guitar voicings. But, it's good to know which notes we have to choose from...
So, since every chord is built by stacking of thirds in a scale, and there are 4 minor scale types, IN THEORY there are 4 versions of each of the 7 chords - one from each type of minor scale, with 6th and 7th corresponding to the minor scale type.
So, for example, you could build a Gm "one chord" from the:
1) Natural minor scale: G, Bb, D, F, A, C, Eb (contains minor 6th and minor 7th)
2) Melodic minor scale: G, Bb, D, F#, A, C, E (contains minor 6 and major 7)
3) Dorian minor: G, Bb, D, F, A, C, E (has major 6 and minor 7)
4) Gm from the harmonic minor scale: G, Bb, D, F#, A, C, Eb (contains minor 6 and major 7)
You can do the same for all 7 chords from each of the seven notes in each of the 4 minor scales in all 12 keys: 4 scales x 7 chords = 28 different types of chords in minor x all 12 keys = 336 different chords to learn how to use!!!! ARGH!!!!
The good news for your practice time is that many many of those THEORETICALLY correct chords sound pretty AWFUL. Some are in fact HORRIBLE (as I said, grown men have often ripped their own heads off rather than hear some of the bizarre chords produced in minor keys. I can't even mention what happens to the players...brrrr). So...we stick to the pretty ones:
Commonly used chords in minor keys:
The I chord (1, b3, 5, etc.) in minor keys is usually a minor 7th or minor 6th with added 9th or 11th. Once in while, especially if the melody has a major 7th in it, we play a minor (major 7th) voicing. If you're not sure if the melody has a major or minor 7th in it, it's always safer to play a minor 6th chord. That's why that's our "go-to" voicing.
The ii chord (2, 4, b6, etc.) is usually a 1/2 diminished chord, though occasionally it can be a minor 7 (2, 4, 6, etc). NOTE: 1/2 diminished chords are notated incorrectly as a minor7b5 throughout this course, due to technical limitations of the scoring/tab program. Sorry!
The III chord (3, 5, b7, etc.) is mostly a major 7 chord with added 6 or 9, but once in a while add in the #5 for a cool mysterious effect (3, 5, 7, etc.).
The iv chord (4, b6, 8, etc.) is usually a minor chord but often it can be IV major if we are building from the melodic minor or jazz minor scales (4, 6, 8, etc.).
The V chord is super important to really get familiar with since there are lots of different versions commonly used. Most often, we play a dominant 7th chord with a b9 and b13 that comes directly from a harmonic minor scale. (5, 7, 9, 11, etc.). Other common V chords are the v minor (5, b7, 9, 11, etc.), often used in 50's/60's rock and folk tunes; another cool one to check out is dom7 13 b9 (5, 7, 9, 11, etc.).
VI chord: There are two "VI chords"; one built on a minor 6th note and one built on a major 6th note. The bVI chord is a major chord (b6, 1, b3, etc.), the VI chord of the key produces a 1/2 diminished 7th chord (6, 1, 3, 5, etc.). This one has a very slick, cool sound while the bVI is more of a pretty, gentle sound.
VII chord: Similarly, there are two "VII chords"; one built on minor 7th note and one built on major 7th note of the key. The bVII chord is sometimes a major/dominant chord (b7, 2, 4, b6, etc.), but the VII chord is a fully diminished Chord (7, 2, 4, 6 - from Harmonic minor).
This is important: The vii chord from harmonic minor is the ONLY diatonic place we can build a diminished chord. OK smarty pants, someone is gonna say, "How about the diminished scale??" And I'll say, "Well, that's not a diatonic scale, is it?? IS IT?? Nope, it's a symmetrical scale!" So, save that one for THE symmetrical scale SG!!!
EXTRA CREDIT! This is SUPER IMPORTANT! The vii chord from melodic minor spells a 1/2 diminished chord (7, 2, 4, b6 etc.), and is super important as it actually spells out a dom. 7 altered chord, which is very common in jazz!!
For example, in the key of C minor the 7 chord from melodic minor (vii chord) is: B, D, F, A, C, Eb, G or 1, b3, b5, b7, b9, b11, b13 - that's alotta flats...
So we build a 1/2 diminished 7 chord w/ flat 9, flat 11 and flat 13. Flat ELEVEN??? b11???? When have you EVER seen or heard about a b11???? Probably never, because if you think this through, a b11 is really just a MAJOR 3rd up an octave. So, re-spelling this mess of notes makes more sense of it all: Let's rename our Eb (b11) as a D# (major 3), then everything else sort of falls into place. B, D, F, A, C, D# instead of Eb, and G = 1, #9, b5, b7, b9, 3, b13 or (shuffling the notes again) 1, 3, b5, #5, b7, b9, #9...this is the complete altered scale/altered chord!!
This is a very useful chord/scale relationship! If you can build B7 altered chord from a C melodic minor scale, then you can PLAY a C melodic minor scale over a B7 altered chord. GET IT??? B7 altered and C melodic minor have THE SAME NOTES!!!!!