Theory - From Classical To Jazz - Part 1

My background is classical piano - I started learning at age seven, and only stopped lessons at 18, when I went to Uni.

Not surprisingly, my understanding of music theory grew from that experience, and playing in rock/pop bands only added a little to my knowledge.

But now I'm playing in a jazz ensemble, and jazz theory, while built on the same theory that I learned all those years ago, has its own unique contributions to music, so I've been trying to get my head around where jazz departs from the classical theory of my childhood.

When you learn classical piano, you learn to play scales and arpeggios. Major scales, harmonic and melodic minor scales, chromatic scales, and arpeggios based around those scales.

You also learn the names of the various degrees in a scale (and the Roman Numerals that are associated with them) - here we have the notes from the C major scale:

When you start to study the theory behind chords, you are introduced to triads:

 

These triads are formed as stacks of three notes - the bottom note is taken from the scale of C major, and additional notes are added at intervals of either a minor or major third (3 or 4 semitones).

It becomes apparent to the student that, except the last triad shown above, that each triad is the 1st, 3rd and 5th from a scale he/she has already learned. (The last triad is the first three notes from a diminished seventh arpeggio.) So the triads are given the following names:

Having learned about triads, the student progresses to cadences:

The plagal and perfect cadences are "endings", where the music resolves to a 'finish'. The interrupted and imperfect cadences sound unfinished and want to resolve.

From here, we extend the triads to include other notes. First of all, we consider 7ths:

Here we notice that when we add the 7th to G or Dm chords (note that we are still working in the key of C major, so the notes in these chords are all taken from the C major scale), the 7th is 10 semitones above the bottom note (the 'root' of the chord), but when we add the 7th to the C chord, it is 11 semitones above the root.

The 7th shown here on the G chord is called a dominant 7th (since G is the dominant of scale). The 7th on the Dm chord is the same interval, but in the context of a minor chord is usually referred to as a minor 7th.  The 7th on the C chord is called a major 7th.

Here is the full set of 7ths based on the scale of C major:

You will notice that the minor and dominant 7ths are simply noted with a 7 after the chord name, but the major 7th is written as 'maj7' - it may also be written as just 'maj', since that implies a 7th, or commonly in jazz and rock music, a triangle is used.

If we continue adding notes to our chords in the same way, we get 9ths, 11ths and 13ths:

At this point, we are still within the domain of classical theory, but moving away from what is common in rock and pop music. We'll add just a couple more chords:

The 6th chord is a basic triad with the 6th added. The 6-9 chord adds a 9th over the top of a 6th chord. These chords, especially the 6-9 chord, are common place in Jazz, but not in rock/pop.

This long-ish post is really just to set the scene and show what's common to classical and jazz theory. In the next post, I'll look at where things start to diverge.