Originally Posted by: Grambo
A chord is made up of the notes 1,3, 5 of A major scale
D chord is made up of the notes 1,3, 5 of D major scale
E chord is made up of the notes 1,3, 5 of E major scale

True. But don't forget that they are all part of a system called the key of A major (i.e. from the A major scale).

The A major chord is the 1st, 3rd, 5th of the A major scale.
The D major chord is the 4th, 6th, 1st of the A major scale.
The E major chord is the 5th, 7th, 2nd of the A major scale.

That's how they are all fundamentally related to one another.

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