Excerpt from ‘Concepts of Jazz' Vol 1. Chapter 1 – The 2-5-1 and associated topics. OK, you're probably right now scratching your head and wondering what in the world a 2-5-1 is. You may have heard of a 1-4-5. You know, chord 1 – chord 4 – chord 5. Countless rock and pop songs are based on this tried and tested chord progression. For jazz music however the 2-5-1 is where it's at! It was the ‘sound' of the day – much like chunky power-chords and bad hair were to the 1980's.
It is the most important and common progression in Jazz music. BASIC HARMONY and SCALETONE SEVENTH'S Before we talk about the 2-5-1 we need to understand a few basics of chord harmony. If you didn't already know, all major and minor keys have a series of chords that we number 1 through to 7. These chords are built off a given major or minor scale. How are chords built off scales I hear you ask? Let's take a look...

If you didn't know, chords are built using notes from any given scale. We start with what is called the root note. This is the note that the chord and scale have as their home base or starting pitch. In the case of a G chord, G is the root note. We then proceed to stack notes on top of the root note in an order known as 3rds – meaning that we start with the 3 rd note in the scale and proceed upwards in that fashion. A Gmaj7 chord for example has the notes G-B-D-F# in it. It contains note 1 (the root note), note 3 (the 3rd note from the root), note 5 (the 3rd note from the 3rd ) and note 7 (the 3rd note from the 5th ) from the G major scale. We could add other notes to our Gmaj7 chord if we wished to. We would simply continue in the same order of stacking 3 rds . We could also flatten (represented by a ‘b') one or more notes, or sharpen (represented by a ‘#') some as well. Also, as you can see, numbers are commonly used to represent scale degrees (1 through to 7 as well as 9, 11 and 13).

This helps us to understand them better and provides an overall grasp of chords, regardless of their key. When talking about chords, we always talk about them in relation to the major scale. If you don't have a handle on the major scale, get cracking! It's THE MOST important scale to know. As I said before, chords are built from scales - For example an Am chord has notes in it that a Bm chord does not.
However the formula or the way we establish what notes belong in the chord does not change. The Am chord will use a set order of notes from the A major scale (1-b3-5), while the Bm chord will use the same order of
notes but this time from the B major scale, it really is that simple!

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