extended triad types

Over the next 3 posts we're going to be discussing extended triad types, i.e. triads in addition to the 4 basic types of major, minor, augmented and diminished (which topic was covered in this post). Perhaps unexpectedly this investigation will lead us into taking up the topic of augmented 6th chords.

If we only concern ourselves with the major and minor scales (both melodic and harmonic), and even if we throw in the harmonic major as well, we'll never encounter any triads beyond the 4 basic ones already mentioned. But this isn't always the case. Take for example the Double Harmonic scale and the triads which form from the scale degrees:


There are major triads (I and II), minor triads (III and IV) and augmented triads (VI) here, but look at the V and VII chords. They don't fit the pattern of the 4 basic types. The issue is that there isn't any ready-made term for either of these, so let's simply name them according to their intervals (which are some form of 3rd and 5th). The V chord is composed of a major 3rd and a diminished 5th, so we could name it a major diminished triad. Likewise the VII chord reveals a structure of a diminished 3rd and a diminished 5th: let's nominate this one a diminished 3rd diminished. And in abbreviated format: maj dim (V) and °3 dim (VII). Here's how they look built on C:



Why are there these different triad types lurking in this scale? Because scale degress 7, 1 and 2 are 2 consecutive minor 2nd intervals, which adds up to a diminished 3rd (and not a full minor 3rd found in the major and minor scales). This accounts for the double flat in the °3 dim triad built on C.

So now armed with this new knowledge you can analyze all of the following scales and you'll find that they contain the 4 basic triad types plus these 2 new "extended" triads: Neapolitan Major, Neapolitan Minor, Double Harmonic (as above), Ionian flat-2 and the Whole Tone Leading. Next time we're going to delve into the whole-half diminished scale and find even more triad types...