Referring to the page 'What chords to use?', it could be said that this progression is in the key of C major (ie these chords can all be derived from the C major scale).

However, by improvising over the track (or even simply looking at it) we can establish that the 'tonal centre' is G (ie the progression 'rests' on the chord of G major and a G note sounds 'strong' throughout the progression).

Many players may regard this piece as being in the key of G major for this reason.

This cannot be so, because if we play the notes of the G major scale over the progression, slowly and listening carefully, we can hear that it doesn't quite fit.
The notes of G major are G, A, B, C, D, E, F#, G.
It is the seventh note of F# that doesn't fit over the F chord.

So it is the notes of the C major scale that fit - C, D, E, F, G, A, B, C - but we need to take into account that the tonal centre of the progression is G.
What we end up with is G, A, B, C, D, E, F, G - the G mixolydian mode scale.

This demonstrates the practicality and simplicity of the modal system.

The above process involved deriving a G scale from the C major scale, and this is what the modal system does. It takes each note of a major scale and regards that note as the tonal centre. Here is what you get, using the C major scale:


You can hear some examples of modal progressions on my Backing Tracks page.

To find some fingerings for modal scales checkout my 'Modes - Where?' page.

You will also find a systematic and simple approach to mastering modal soloing / playing on the 'Modes - Where?' page