The Basics of Music Theory - Part 6 (Diatonic Triads)

In The Basics of Music Theory - Part 5 (Triads and Inversions) the concept of chords built upon a base triad was discussed. That is to say, the initial triad was derived from the major key and then each note other than the root was mutated to give the other triads available. In this installment the triads are build based not he root of each note of a major scale.

Diatonic, in music, any stepwise arrangement of the seven “natural” pitches (scale degrees) forming an octave without altering the established pattern of a key or mode–in particular, the major and natural minor scales.
— Encyclopedia Britannica

The above definition gives a workable definition to the work diatonic. Therefore, if the chords only use notes held within the given scale, then the chords become diatonic. The important takeaway from this is that every major key has the same pattern of whole steps and half steps. This means that every major key has the same pattern of diatonic chords. The triads for the key are built by staking 3rds on top of each other from the key. These diatonic triads lay the groundwork for the harmonies that encompass that particular key.

Scale Degree 1 2 3 4 5 6 7
Harmony I ii iii IV V vi viio
Triad Type Maj min min Maj Maj min dim

Take special note in the above table that the upper case Roman numerals are used for major harmonies, and the lower case are used for minor harmonies. The added "o" as a superscript to the "vii" indicates the diminished harmony.

Below are the diatonic triads found in the key of C major. These are all in root position (remember lowest note is the root) for clarification. You could use any key in the key signature and begin on the root of that key to give you every triad in every diatonic key if you so desired.


Next time we will look at using this knowledge to using more complex chords. If you missed anything from before, then follow this link (The Basics of Music Theory -  Part 5 (Triads and Inversions)) to the previous installment of this series.

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