The melodic minors should really be the name of every junior school choir, but in actual fact, the melodic minor scale is like an eccentric cousin of the natural and harmonic variants.
You can use two methods to construct our natural and harmonic minors: the derivative method (building the scale according to the intervals between each note within the scale) and the definitive method (altering the notes from its major equivalent).
The melodic minor scale can be built using similar methods, but the main thing that sets it apart from its two relatives is that, traditionally, it uses one pattern when it’s ascending (going up the keyboard), and another when descending (going down the keyboard).
The main reason the melodic minor scale came about was as a way to reduce the size of the interval between the 6th and 7th degrees of the harmonic minor scale. This three-semitone gap made it hard for early singers to wrap their vocal cords around compositions that used it. By also sharpening the 6th degree, the intervals between the notes in the scale became a more manageable mix of tones and semitones - a melodically smoother scale, hence the name.
When using the melodic minor in modern music, the tendency is to throw the rulebook out of the window and just use the ascending form in both directions. It’s an interesting-sounding scale with a construction that can make it a bit awkward to work with, but there are certain areas - especially jazz - where it really shines.
With our case for this curious scale made, check out the video to discover one of music’s more mysterious misfits.