Originally Posted by FerrariT
What I don't understand is how the chords work within the scale.
Say if the melody was composed in the scale Dm what determines the chords you are able to use?
Any links to redirect me?
Kind of complex question, but I tried my best below. I used subheadings for clarity. Hopefully this helps. Major Keys and Their Relative Minors
Regarding major and minors, it is usually sufficient to start by just learning the basics of major keys, and consider minor chords as simply darker sounding rearrangements of those major keys.
This is because every major key has a relative minor, and, for beginner purposes, the relative minor is identical to the major. The only difference is the minor centers around the minor 6th (vi) of the major key and sounds darker because of this.
So for example:
key of C ~ relative key of Am (since Am is the vi chord in the key of C...)
key of E ~ relative key of C#m (since C#m is the vi chord in the key of E...)
key of F ~ relative key of Dm (since Dm is the vi chord in the key of F...)
key of G ~ relative key of Em (since Em is the vi chord in the key of G...)
So if someone said 'play some chords in the key of Am', playing chords in the key of C major would functionally be the same thing.
So again, for starters, I think it's generally easier to think purely in major key terms and branch out from there. Also, since we're dealing with piano, it's probably easiest to start with the key of C major, since it is basically just 'white keys only'.
So let's start by explaining only C major, and you can hopefully go from there with practice. The Seven Basic Chords in a Key
In the key of C major, you are 'allowed' the following basic 7 notes and chords: I = C = C E G
ii = Dm = D F A
iii = Em = E G B
IV = F = F A C
V = G = G B D
vi = Am = A C E
vii-dim = Bm dim = B D F
With roman numerals, capitals denote major chords, lower case denote minor chords. Roman numerals are used because they can describe progressions in any key, whatever you choose.
So if someone asked you to play a I V vi IV in C, you'd play C G Am F.
Or if you wanted something darker (and technically in relative Am) like a vi IV I V, you'd play Am F C G.
For other common keys, here is a table of what the 7 basic chords work out to: MMC presents... Dansm's Guitar Chord Theory: Chords in Major Keys
(good site - where I learned most of my basic theory from way back...)
Most really experienced players can 'translate' from key to key in their head from the roman numerals, but no one should expect that starting out.
When playing in a key, you are never limited to purely major/minor chords. There are an almost endless number of ways you can 'spruce up' the basic chords by adding/omitting notes. So long as the notes you add fit the scale of the key you're in, they're fine to fit in that key.
The most common in jazz/soul/r&b are 7th chords. To make a 7th chord, just count the notes of your scale up from the root of the chord you're playing and add the 7th when you get to it.
Depending on which chord you're dealing with in a given key, there are two basic types of 7ths you'll end up with - dominant/minor 7ths and major 7ths. You call it a maj7 when the 7th comes out to just 1 semitone lower than the root of that chord. You call it a dominant/minor 7th when the 7th comes out to two semitones lower than the root of that chord.
So in a given key (eg. C again for simplicity) you get:
I maj7 = Cmaj7 = C E G B
ii min7 = Dm7 = D F A C
iii min7 = Em7 = E G B D
IV maj7 = Fmaj7 = F A C E
V dom7 = G7 = G B D F
vi min7 = Am7 = A C E G
vii-dim min7 = Bdim min7 = B D F A
If you look at all the chords and notes above, you'll notice all notes/chords fit the C scale perfectly, and thus all chords are still in key. Other Chords
Other chords are built the same way as 7ths. For example, if you want a 6th chord, simply add the 6th note you get counting up from the root of that chord in key. eg. The 6th of a G in the key of C is an E (G6 = G B D E).
A 9th chord adds the 9th counting up from the root. eg. for C in key of C, this would be D (C9 = C E G D).
You can also do things like omit the third to get 5th chords aka power chords (C5 = C G C). Or if you add in a 2nd or 4th you get sus2 or sus4 cords (Csus2 = C G D || Csus4 = C F G ). Going Outside of Key
After you've got all that down and can perfect playing in a key, try adding chords that don't technically fit but are from related keys so may sound good.
eg. Throwing an Fmaj7 (from the key of C) into a key of G progression often sounds good because the keys of C and G are quite close in nature.
Or again, in latin, they usually play the minor 3rd chord (iii) as a major third (III) to give progressions like, in key of C: Am G E F (vi IV III V) instead of Am G Em F (vi IV iii V) as it technically should be.
And with everything, of course, experiment, and have fun.