The major and minor modes are actually modern modes. In the fourth century,
there were many modes used in the church. There is a mode for every white
key on the piano just like the minor we have just studied which begins
on an A. Its old modal name is actually aeolian.
By starting a scale on each white key and using only white keys, you can
play the other modes. For example, if you start on a D and play up to the
next D using only white keys, you will be playing the dorian scale. Notice
that the half steps in the scale have moved to their "dorian" scale positions.
For our purposes, we only need to know that these old modes coalesced
into the two modes we now know as major and minor. The major mode has
only one form but the minor mode has several forms.
The minor scale form we have just learned is called the "natural" minor because it is the form that naturally results from the key signature when you begin on the sixth degree of the major scale. The natural minor is actually not the most common form of the minor scale. By 1600, music became "tonal" rather than "modal" and is now characterized by the tonal directionality we feel when we sing the musical tails we are studying. Notes in the tonal scale have a hierarchy not present in the modal scale (e.g. the tonic is more stable than the seventh degree, etc.).
The following changes which are made to the natural minor scale are the result of tonal pressures already present in the major scale on the more modal minor scale.
Before continuing we should address a new terminology practice. To help distinguish between major and minor chords when using roman numerals, major chords are giving upper case roman numerals (e.g. I,V) while minor chords are given lower case roman numerals (e.g. ii,vi).
Harmonic Minor
One of the most important characteristics in a tonal scale is the half
step interval from the seventh to the eighth (tonic) notes of the scale.
The major scale has this half step but the minor scale has a whole step.
Raising the seventh note of the natural minor scale gives us this melodic
tonal characteristic which reinforces the stability of the tonic degree.
However, more importantly, the chord that usually precedes
the tonic (I) chord is the dominant (V) chord. This chord in the major
scale is also a major chord but in the natural minor, this chord is minor.
Moving from a minor v (chord built on the fifth degree) chord to the
tonic is not as convincing as moving from a major V chord to the tonic.
We can make the minor v chord a major V chord by raising the middle note
of the triad.
Interestingly enough, the middle note of the v chord is also the seventh degree of the minor scale! So by raising the seventh degree, we solve both the melodic tonal problem as well as the even more important harmonic one. This new scale form is appropriately called the "harmonic" minor.
Although the harmonic scale form solves some tonal problems, it also creates a new one. The distance between the sixth and newly raised seventh degrees of the scale is quite difficult to sing. It is now larger than a whole step which is normally the largest distance to separate scale notes. The interval is an augmented second which might remind you of a snake charmer melody.
The solution to this new problem is simply to also raise the sixth degree
when singing up the scale and lowering both the sixth and seventh degrees
when singing down the scale. Notice the blue animated notes which show
the descending version of the scale. Also, the scale is only played down
to the 5th degree because the remaining notes are all the same as the
ascending version.
The notes that were raised as the scale ascended are lowered to their
natural minor form when the scale descends. This change is also for melodic
reasons. The descending scale is easier to sing with the lowered notes
because they tend to "lead" down to the fifth degree of the
scale. This is just the reverse of the raised ascending notes which tend
to "lead" up to the tonic. The fact that there is a difference
between the ascending and descending melodic minor scales is a distinguishing
feature of this scale. The natural and harmonic minor scales have the
same form, ascending and descending. Therefore, if you hear the descending
scale different than the ascending scale, it must be melodic minor. Listen
to the above examples and notice their distinguishing features.
So Which Minor Is It?
When a musical selection is in minor, it is actually in all of the minors discussed here. The composer slips as needed into whichever minor is appropriate at the moment. Sometimes the composer may want a more modal sound and stay mostly in the natural minor and only slip into the harmonic minor at phrase endings.
Likewise, as the composed melody ascends, the composer may use the ascending melodic minor to avoid the awkward augmented second only to slip back into the natural minor as the melody descends.
A minor piece of music is therefore simply in the minor rather than one of these particular forms. When looking at a piece of music, you can look for the occasionally raised sixth and seventh degrees of the scale to help you decide if the mode is major or minor. Even though the key signature for both the major and relative minor is the same, only the minor would have these telltale signs.
