C Lydian Augmented
The 4th raised, the 5th raised — the brightest scale there is.
Lydian already raises the 4th. Lydian augmented raises the 5th as well. Nothing in common practice is brighter, and there is no ordinary chord it fits — which is exactly what makes it useful.
Two raised degrees
C Lydian augmented is C D E F# G# A B. Compared with C major, both the 4th and the 5th are raised. Every alteration in the scale pushes upward; there is not a single flattened note in it.
- The #4 (F#) comes from Lydian.
- The #5 (G#) is the extra one.
- No note in the scale is lowered — hence the brightness.
The third mode of melodic minor
It is A melodic minor played from C. That is the practical way to find it on the neck: take any melodic minor shape and treat its ♭3 as the new root.
- C Lydian augmented = A melodic minor from C.
- Melodic minor from the ♭3 gives you this scale.
- One shape family, three useful modes.
Over maj7#5
The chord is Cmaj7#5. Over a plain Cmaj7 the G# will fight the G in the chord, so it needs a chord that actually contains the raised 5th. It is a colour for a specific harmony, not a general-purpose major scale.
- It fits Cmaj7#5 and Cmaj7#11#5.
- Over a plain Cmaj7 the #5 clashes with the 5.
- Use it to make a tonic major chord sound suspended and floating.
Two raised notes and nothing lowered: the brightest seven notes available, and they need a chord willing to hold them.
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