The octatonic scale is not new to guitarists, in jazz it’s commonly known as the diminished scale because it is essentially two diminished seventh chords superimposed to form an 8-note scale. Like the whole-tone scale, Messiaen did not invent it, but he categorized it as the second mode of limited transposition. The scale simply alternates between whole and half steps, and you can begin with either a half or a whole step.
This scale has three transpositions and, comme toujours, no tonic:
Consider the first transposition (E, F#, G, A, Bb, C, C#, D#) in terms of two diminished seventh chords:
E G Bb Db F# A C Eb
Also note a few major/minor triads that are native to the scale:
A C# E (G)A C EC E G (Bb)C Eb GEb G Bb (Db)Eb Gb BbF# A# C# (E)F# A C#A C# E (G)
These can act as pivot chords for modulation into and out of the octatonic scale from any major or minor key that has one of these chords. Each major chord can also act as a dominant 7th, still native to the octatonic scale (noted in parenthesis).
To me, the octatonic is far more interesting than the whole-tone – it can be easily incorporated into a piece of tonal music with these major/minor triads, and it sounds much richer than the whole-tone scale. The octatonic scale also lends itself very well to guitar, and has really helped me break out of some ruts by challenging my muscle-memory comfort zone. Surely all guitarists know the feeling – you rely too much on your fingers, allowing them to think for you, and the bastards only want to play what they’re used to. They defy us and any attempts to change their old habits, crapping on your creativity in the process. Sometimes these episodes last for months, and I’ve found the only way to fix the problem is to introduce radically new material, and play it exclusively. A musical shock-and-awe which your body will attempt to reject, but a necessary step towards progress. Upon returning to your old habits, you’ll see everything in a delicious new limelight, and fascinating new patterns you’ve never noticed before will suddenly emerge.
The octatonic is one of my favorites – I highly recommend it to anyone with an open mind looking to open it up a bit more.