Chords are built from scales. If you want a C Major chord, for instance, you must build it from the C Major scale. In fact, all of the available chords for any given key signature can be built from its scale.
Let’s use the key of C for our example. What we want to do is find all of the major and minor chords available to us in the key of C. We’ll start by looking at our C Major scale:
C Major: C-D-E-F-G-A-B-C
First, let’s find C Major. Major chords are built from the root, third and fifth degrees of a scale. In this case, we have C, E and G in these positions, so a C Major chord consists of the notes C-E-G played simultaneously.
Now, what about all of the other chords in the key? Just count over in the same fashion, but look at the ‘root’ as beginning from the next degree up:
Dminor: D-F-A
Eminor: E-G-B
F major: F-A-C
G major: G-B-D
A minor: A-C-E
B diminished: B-D-F
You might wonder how you know which chords are major, minor or diminished. One thing you can count on is that the above pattern holds for every major key. Let’s compare the key of C to the key of D for a moment:
C Major: C-D-E-F-G-A-B-C
D Major: D-E-F#-G-A-B-C#-D
The key of D has two sharps (F and C). D-F#-A is a D Major chord.
The rule for minor chords, though, is that you take a Major chord and flatten its third. So, if you flatten F# to F, you end up with a D Minor chord. In the key of C Major, there are already no sharps.
In other words, the ‘third’ is already flattened. That’s why you have a D Minor chord in that key. The concept of ‘shared notes’ versus sharps/flats among keys is behind all of the chord types within a given key, be it Major, Minor or Diminished.
The system for finding the sharps in a key is called The Cycle of Fifths, and the system for determining the flats is called The Cycle of Fourths. Some people prefer to use the word ‘circle’ instead of ‘cycle’ because the keys are diagrammed along a circle.
It’s an important concept, but a bit too detailed to go into in this report. You can, however, find a very good explanation of The Cycle of Fifths/Fourths on Wikipedia:
Last, but not least, you can grab a very nice printable chord chart which will show you the exact positions and shapes of the most commonly used chords from a site called ‘Chordie’:
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