A chord consists out of different notes...
A basic chord, like C consists out of the 1st, 3rd and 5th note of its scale.
For C that means : C E and G .
If these notes fit into a scale like G : G A B C D E F# G (they do) you can play it.
When you play this chord over a G mayor scale (see above) then you'll be playing the IV chord in this scale. This is a mayor chord.

Nw lets say you want an A mayor chrord in it.
This chord consists of A C# and E.
As you can see oin the given G mayor scale.. the C# isnt there... so you lower the 3rd note in this chord, giving you a minor chord. A C E.

You can also do this with 1 3 5 7 ( seventh chords) and all srts of different chords.

Correct me if im wrong or when it needs more info

hope it helped
Playing since december 2004
Quote by BloodMoon666

*sports commentator voice*
And this thread is over!

Wonderful match by TS but in the end simply overwhelmed by the pure skill and simplicity of unfluffed. A true professional in action.
Take any major scale u want, ill use C major as an example to keep things simple and then apply this pattern. Major Minor Minor Major Major Minor Diminished.
If u apply that to CDEFGAB u get C Dm Em F G Am Bdim.

As for other chords, figure out the notes that make up the chord and then compare them to the scale ur using. Eg. An Fmaj7 fits into the key of C because the notes that make up an Fmaj7 (FACE) all appear in the C major scale. An Amaj7 (A C# E G#) does not fit into the key of C because it contains notes that arent in the C major scale (C# and G#).