Musical Composition, Theory and Songwriting/music
We have only one kind of Major sclae but thre kinds of minor scales. Why is it so? Do we really need three minor scales?
ANSWER: There is some debate as to why we have the natural, harmonic, and melodic minor scales and how they came to be, although here is a fairly common interpretation:
The natural minor scale, also called pure minor scale, was given the name due to it containing the exact same notes as its relative major scale. It is unaltered, pure, or in a natural form.
The harmonic minor scale, which is similar to the natural minor scale only with a raised 7th scale degree, is believed to have been altered for the sake of harmony, as in the harmonic structure. The inclination here is that the chord progression that includes movement from a V to I chord will benefit from having the leading tone in the V chord, which is that raised 7th.
The melodic minor scale is melodic in nature, and some believe it to be a development from the harmonic minor scale, thus raising the 6th scale degree, so as to even out the intervals between notes in the scale. The reason for the return to the natural minor scale degrees when descending could be that while an ascending melodic passage might alter pitches by raising them, descending melodic passages might include altered pitches that have been lowered. The reason could be simply for melodic effect.
You mentioned that we have only one kind of major scale. Technically, we have many, when considering more than the standard major scale that consists of these whole (W) and half (H) steps: WWHWWWH. Likewise, there are multiple minor scales, even of just the natural minor variety. The key here is the use of modes.
CDEFGABC = Ionian (also Major), a major-type scale
DEFGABCD = Dorian, a minor-type scale
EFGABCDE = Phrygian, a minor-type scale
FGABCDEF = Lydian, a major-type scale
GABCDEFG = Mixolydian, a major-type scale
ABCDEFGA = Aeolian (also Natural/Pure Minor), a minor-type scale
BCDEFGAB = Locrian, a minor-type scale
Note that the 3rd scale degree is either a major 3rd or minor 3rd (interval from the 1st scale degree). It is a major-type scale with a major 3rd and a minor-type scale with a minor 3rd.
That also excludes the use of altered scales and modes, and is restricted to the use of scales consisting of 7 separate pitches, as opposed to fewer or more (i.e., pentatonic and octatonic). It also excludes the use of pitches that do not adhere to our standard tuning system, such as microtones.
Our alphabet and words are to sentences, paragraphs, and stories, as individual notes and scales (and chords) are to phrases, sections (and movements), and entire compositions.
Imagine different scales as being the words needed to form musical sentences. Likewise, the notes in those scales are like the letters in words. Sometimes you use alternate spellings, and sometimes you change the meaning of a word based on the letters that you use with it.
Best of luck!
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QUESTION: I had a teacher who told me that I don't need to bother about the 7 modes unless I would be playing medieval or church music. Are you saying something different?
There are technically more than 7 modes, although the 7 that I listed are the first set of modes that students usually learn when learning additional scales. Those modes do not apply exclusively to medieval or church music, they can also be applied to jazz, modern/contemporary, or any of a number of styles of music.
I provided the information about modes to take you to the next step, while the initial information that I provided specifically addresses your original question.
If you are concerned about whether or not your teacher prefers a certain answer, then I encourage you to direct your questions to your teacher.
Best of luck.