7th and 6th-degree notes for a piece in a minor key

Question

For a piece in a minor key, do we raise all 7th and 6th-degree notes by a half step (with respect to having only the key signature)? I know that for harmonic minor scales only the 7th-degree notes are raised while for melodic minor scales both 6th and 7th-degree notes are raised compared to natural minor scales, so I am asking with regard to pieces in a minor scale.

In other words, which of the following is/are true, or it depends on the composer?

• ALL 7th-degree notes raised by a half step
• SOME 7th-degree notes raised by a half step
• ALL 6th-degree notes raised by a half step
• SOME 6th-degree notes raised by a half step
• ALL 7th AND 6th-degree notes raised by a half step
• SOME 7th or 6th-degree notes raised by a half step

Answer 1

Have you ever heard of J.S. Bach? Just have a look at one of his minor pieces: Inventions (e.g. D-minor, G-minor)), Preludes and Fugues (WTC) or his Ricercare. (In the same measure one voice can have a raised 6th and 7h, while the other voice is lowered respectively natural. You will find thousands of examples of what like Aaron says in his comment:

Maybe you are confused by the modes. As you may know in the melodic scale (leading up) the 6th and 7th are raised and (when leading down) they are natural. The harmonic scale has a one and a half step between 6-7, (up and down) because only the 7th is raised (leading tone!).

Bear in mind that there are "minor" modes like Dorian that has only a "raised" 6th.

If you want to learn more about the modes you can look up here in this SE. (They are the historical scales before the western major - minor system was established.

Ricercare:

Answer 2

Sometimes the sixth is raised, sometimes the seventh, sometimes both. It's entirely up to the composer.
If you are the composer you can write whatever you want.

Answer 3

As with all music, do what you like. Others may not like what you do, though.

The basic premise with minor keys is that originally, using the natural minor notes, there was no leading note - the note that is only one semitone below the tonic in major keys. So it was felt that in rder to achieve that pull towards the tonic, the normally flattened 7th note would sound better raised. Hence the harmonic minor scale set of notes.

That left us with a huge (comparably) gap between the 6th and 7th notes - in key Am, the tone-and-a-half interval between the 6th (F)and the new 7th (G♯). To solve that, a raised 6th came in to save the day. It was most useful/important for melodies - hence the melodic minor. Melodies would favour the ascending melodic minor notes when ascending, but the natural minor set of notes still sounded fine when the melody descended. Hence the odd melodic minor scale - differing from the major only by the m3 ascending, and using the natural minor notes descending.

There is not a 'rule' as you hope - although a lot of classical music did use the idea from the melodic minor, but these days, it's nowhere near as prevalent. In fact, if you are a jazzer, you'll more likely use the rising melodic notes whichever way the melody goes, in a minor piece.

Answer 4

There is no iron clad rule for this. The 7th MUST be raised to create a cadence in the minor key, V7 --> i. This is a device that is very much favored in Western music. The composer can write melody lines that stay on the natural minor (no raised 6th and 7th) for a while then introduce the #7 only when they want to finish the musical idea with a cadence.

Understanding why the 7th is raised is key to understanding why it is used and why it is entirely possible to NOT use it all the time.

It should also be noted that the 6th and 7th are only raised on ascending melodic lines and are made natural on descending melodic lines. At least in classical music this is the device used. One encounters a "Jazz melodic minor" scale that keeps the 6th and 7th degrees raised.

Answer 5

There are a few very common procedures. I listed some in my answer to Understanding minor key harmony

Basically, steps 6 and 7 are mutable. Most classical composers followed those I mentioned. (These also work well in country, Latin, pop, jazz, etc.) Often, different voices (melody and bass in popular oriented music) may use different versions of the same note simultaneously.