"Good music theory should always describe the way music sounds. One exception in traditional music theory is the augmented 6th chord. It sounds like a dominant 7th but is labeled a 6th chord because its spelling includes the interval of an augmented 6th. Adding to the confusion is that 3 geographical labels are often attached to these chords. The augmented 6th chord is usually found in 1st inversion."
Jazz theory resources by Bert Ligon