Before continuing several very important points must be made:
1. Minor is considered to be only one entity. It is not appropriate to speak
of “three separate minor scales,” as if they are inherently different
species.
2. Although one entity, minor has three distinct
forms
, Natural,
Harmonic, and Melodic. These forms evolved to accommodate musical
and compositional needs over the evolutionary history of Western
music.
3. The three forms have distinct properties:
a. Natural (or Pure) Minor has no
Leading Tone
. This was considered to
be an inherent weakness or flaw.
b. Harmonic Minor seeks to correct this weakness by raising the
seventh scale degree, artificially creating a
Leading Tone
. This in
turn generates a
melodic
flaw in the gap between scale degrees 6
and 7.
c. This melodic flaw was corrected by raising the sixth scale degree
(in the presence of the raised seventh scale degree). Since this
yields a second tetrachord equivalent to its Major scale
counterpart, this process is undone in its descending form by
reverting to Natural Minor.
4. Lastly, Harmonic minor is the expected, normal form of Minor used by
composers in practical composition.
Composers seemed to require the motion from the
Leading Tone
to the
Tonic
. Just as
much, they seemed to favor the naturally occurring sixth scale degree, the
Submediant
, “falling” to the
Dominant
. In the study of music theory,
expect
to see,
expect
to hear, and
expect
to use the Harmonic form of Minor. The unique properties
of the other forms are used sparingly and are subject to conditions for their use.
In summary, major and minor scales form the fundamental source sets, and
therefore the basis of the compositional language in Common Practice music. All
the great music of the recognized master composers employed these same
constructs as the basic elements of their compositional language.
Chapter 3 The Foundations Scale-Steps and Scales
3.2 Heptatonic Scales: The Major Scale, The Three Forms of the Minor Scale
100