The scale and it's harmonic system known as Melodic Minor (aka: Jazz Minor, Ascending Melodic Minor, Ionian b3, etc.) is probably the most misunderstood and under digested of the traditional diatonic derived scale systems being used in improvised music.
Many students, and professionals alike, tend to freeze up like they saw Frankenstein when presented with chord symbols or mode choices native to Melodic Minor, or for that matter, not native to Major. Most of us have been taught to view any altered chord type as an altered form of it's Major counterpart.
For example, let's look at Eb Maj7+5 (Eb - G - B - D). We take an Eb Major 7 chord (Eb - G - Bb - D) and raise the 5th a half step (Bb to B), right?. But now it no longer belongs to either the Major key of Eb or Bb, or for that matter, any Major mother scale.
So where then does it belong? Who is this baby's mother and where is she? The idea of taking a chord from the Major scale and altering an element of that chord is, in itself, not totally misguided, but....!
Why don't we take a look at the whole Major scale and see if we can alter one of it's elements instead. In the key of C, lowering it's third degree (E) a half step (to Eb) might be a great place to start.
Now, the "E" becomes an "Eb" (Maj. 3rd to min. 3rd) and our C major scale becomes C Ascending Melodic Minor, or just plain C Melodic Minor (we can drop the "ascending" part because we're going back down the same way we came up).
Not so coincidentally, our Eb7+5 chord, now has a home. The baby has found it's mother and it now resides on the third degree of the C Melodic Minor scale. It's address could read, "No.3, Eb Lydian Augmented" (see graphic).
So now that we've given our baby a home, let's take the tour. The first thing we notice is that by just lowering that major third a half step, we've totally messed up the internal structure & interval relationship of the Major Scale. "Achh ja, Igor! Das ist sehr gut!"
Not only is it no longer a "Major" scale, but it also no longer possesses that all important half step leading tone between scale steps 3 & 4 ("Vee have now cutted his brraaaaiiinn!").
By lowering that 3rd, we've also created a row of 5 notes separated by whole tones (Eb - B), or one note short of a complete whole tone scale. The lowered 3rd also gives us (starting from the note A below, up to F), six out the eight notes of a full diminished scale. "Oh Mein Gott, Igor! Was keint of hybrid, mutant, f-r-r-reakazoid haben wir hier gemacht ?!"
Only to discover still, that our creation has yielded not one, but two tritones (F-B & Eb-A)!! Tritones? Flatted 5ths? You mean.......the........ devil's interval!?
It seems that now, we have truly unleashed.......M.M!...... Major's Evil Twin!
M.M. is a Mon-stah!!
"Arrrgh! I have come to alter your scales"
Stay tuned for Pt. 2 and beyond, of this thrilling Chiller (or is it chilling Thriller?), and learn how M.M. & Major, reconcile, get married, spawn, and live happily ever after in your horn!!
For an in depth look at Melodic Minor harmony, check out "The Melodic Minor Handbook".
"Slick Licks That Stick!" a 177 page PDF eBook, contains supplemental MM material not found in the "Handbook".
Available from jazzbooks.com