I've recently been getting into transposing songs into their parallel major / minor keys. I've recently tried the Princess Mononoke Theme by Joe Hisaishi, but it just sounds weird when we transpose it from minor to major.
I understand that the second measure, in D major, contains a tritone in the melody line, causing it to sound bad. However, are there any music theory rules around when a song would sound bad in its parallel major / minor key?
I see that Tim already gave my answer:
If you have only the harmony of the classical cadence tonic, dominant subdominant a transcription to major from minor and vice versa is no problem.
But here we have somewhat a phrygian cadence. (only that there's not a major V) It's almost impossible to transcript to the parallel key if you don't keep the VII major chord unchainged (as it has been already a major in the original version.
Another possibility would be to adapt the melody (like it is use in classical sonatas aswell in the subject of a fuga:
Instead of transforming the theme la mimimire mi mi sore to do sososofa so so ti fa you could transform it this way: so mimimire mi mi sore That means instead of transcribing to the parallel key Dm -> D of you change to the relative key.
And this here is actually the link I was looking for: min.5:11
Maybe the point with the problem you have will be explained to you https://www.ars-nova.com/cpmanual/alteredmodes.htm
where it's said:
(2) In descending, the upper note of the mode's tritone (B when untransposed) was often flatted to avoid the tritone if the lower note (F when untransposed) was present. In ascending, the same problem was solved by raising the lower pitch.
(3) Upper auxiliary tones (upper neighbor tones) were typically flatted in practice, though generally not written that way.
(4) The sixth degree in a minor mode could be raised if moving to or from a raised seventh degree, in order to avoid a melodic augmented second. This is the basis of the modern "melodic minor." In certain cases it might be necessary to raise another degree to avoid the aug. 2nd, for example in a Phrygian final cadence where the third is raised to major and a voice passes from the second degree to the raised third degree.
(5) Internal cadences could be formed on any degree, with one tone raised to form a leading-tone. But the modes had characteristic differences in the tones on which such cadences were formed. Jeppeson identifies these patterns, with the three most common cadences as follows ...
It's always easier to play a song in its parallel key when only the 3 main chords - I IV V or i iv V (or v) are in the song.
Thus answering - when there are more than the 3 main chords. Although, it's entirely possible to harmonise in the parallel key, but will involve judicious choice of harmonies.
I'm probably repeating a bit, in different words, what the previous answers say.
When changing from major to minor (or vice versa), you keep the key note but change the mode, not necessarily the chords. Changing from major to minor doesn't mean just swapping chords (such as i for I, ii0 for ii, III for iii, iv for IV, v for V, VI for vi, and VII for vii0). For example, (going from major to minor) one may wish to keep the V (or V7) at cadence points but non-cadential V chords usually become minor (passing chords and the like and perhaps some half-cadences or cadence patterns that do not end phrases). Several chromatic chords (Neapolitan, French, Italian, and German Sixths for example) are the same in major and minor; these probably should kept the same. Some diminished chords (made of three minor thirds is an example) stay the same but a half-diminished chord often can become fully diminished. Dominant ninths occur with a lowered 6th step in either major or minor but a chord like G-B-D-F-A can take the Bb sometimes.
Augmented chords may or may not change because of voice leading; it depends on the chords around them. The ii6 in major sounds good as a ii06 in minor; it's sometimes used this way even in major keys at cadences.
Rather often, classical era (Haydn, Mozart, Beethoven, Schubert, etc.) pieces do repeat passages in "the other mode" somewhere (exposition, development, recap) so these may give one an idea what has been used in the past.
Still, it's fun to do on the fly. I've done it with country-western pieces that were simple enough (especially waltzes) and the audience didn't notice.
Melodies that work well in both modes tend to emphasize musical features common to the modes, such as stepwise motion, the stability of scale degrees 1, 3, and 5, chord progressions using primary triads, sequences by descending fifth or third, etc. Examples can be found in any of Bach's fugue subjects.
Melodies that work badly in the opposite mode tend to emphasize musical features that differ in both modes, such as
So, for instance, the hymn tune "Be Thou My Vision," which, like most Irish folk music, is mostly pentatonic, does not work well in minor, while "A Mighty Fortress is Our God," which stresses scale degrees 1 and 5, works fine in minor (but don't get caught playing it that way in church...)
Maybe the rule is: it sounds bad if you try to fit the changed melody into an unsuitable harmony?
What comes to the example you gave, I don't see a big problem.
With an ascending bass on the first line:
With a descending bass on the first line:
I'm not entirely happy with the last two bars of the first line, but someone else can suggest something better. The point is, listen to the melody and harmonize it according to its nature.
