Introduction to Chord Theory: Major Diatonics
Here is a brief lesson introducing the basics of chord theory. This lesson will deal only with triads, larger chords will be addressed later.
For the purpose of elementary chord theory, all chords are constructed by stacking intervals of thirds. In addition to this basic rule, it is also a safe bet that you will (for the most part) encounter 4 types of chords: Major, minor, diminished, and augmented.
When you hear a chord, you hear each note and interval from the bottom up. The bass note is what actually makes the chord identifiable. In root position (inversions will be addressed later as well) you start with a single note, the third above that, and another third above that one, which also happens to be a fifth above tonic.
Starting from the bottom:
Major: Major third + minor third
Minor: Minor third + major third
Diminished: Minor third + minor third
Augmented: Major third + major third
Get it? It is quite simple actually. Take for example, a chord with the tonic of C. A C major chord would consist of a major third above C, which is E, and a minor third above E, which is G. A C major chord would be spelled out as [C-E-G]. On the other hand, a C minor chord is the opposite interval combination, a minor third with a major third on top. This would give you [C-Eb-G] which is C minor. How is that for easy?
So, let’s take this one step further. Every major scale creates the “perfect storm” so to speak that allows for each note to have an appointed chord. These chords will never change unless accidentals from outside the key are introduced. Take for example the key of A major, [A-B-C#-D-E-F#-G#-A]. To find the corresponding chord type for each note simply take that note and add every other note after. Take the first note, A, and add C# and E … This gives you an A major chord. [B-D-F#] is a B minor chord, etc… Lucky for you though, since every major scale is constructed from the same combination of intervals, they share a common combination of diatonic (naturally occurring) chords.
In A major
A (I)- Major
B (ii)- Minor
C# (iii)- Minor
D (IV)- Major
E (V)- Major
F# (vi)- Minor
G# (vii*)- Diminished
Remember this and you will always know what chords you have at your disposal when working within a given key: I, IV, and V are always major, ii, iii, and vi are always minor, and vii* is diminished. Learn it, love it, make it your own, because you will always use it.
Disclaimer: This only works in major keys! The same system applies to minor keys, but it turns out differently. I will address this in a separate lesson.