Start with the Natural Minor Scale
Everything begins with the natural minor (Aeolian) scale.
In A natural minor, the notes are:
A – B – C – D – E – F – G – A
Formula:
1 – 2 –b3 – 4 – 5 – b6 – b7
Both harmonic and melodic minor are simply modifications of this scale.

Harmonic Minor: The Exotic Sound
The harmonic minor scale raises only the 7th degree.
A Harmonic Minor
A – B – C – D – E – F – G♯ – A
Formula:
1 – 2 – b3 – 4 – 5 – b6 – 7
The raised 7th creates a strong pull back to the root because the leading tone is only a half step below the tonic.
What Makes It Sound Different?
The biggest feature is the interval between the b6 and the raised 7.
In A harmonic minor:
F → G♯
This is an augmented second.
That unique leap is what makes harmonic minor instantly recognizable.

Melodic Minor: The Smooth Alternative
The melodic minor scale raises both the 6th and 7th degrees.
A Melodic Minor
A – B – C – D – E – F♯ – G♯ – A
Formula:
1 – 2 – b3 – 4 – 5 – 6 – 7
By raising both notes, the awkward augmented second disappears.
Instead, the top of the scale moves smoothly:
F♯ → G♯ → A
This creates a much more flowing melodic sound.

A Quick Note About Classical Theory
Traditional classical music teaches melodic minor differently:
Ascending: 1 2 b3 4 5 6 7
Descending: 1 b7 b6 5 4 b3 2 1 (natural minor)
Modern guitarists and jazz musicians almost always use the same melodic minor scale both ascending and descending, which is what you'll hear in fusion, jazz, and modern rock.
SIDE-BY-SIDE COMPARISON