I'm not sure what your question is. Borrowed chords are borrowed from a given tonic's parallel mode/key.
C major and
C minor are parallel keys and borrow chords from each other.
But you bring in the idea of a relative key.
Normally from the key
A minor you would borrow chords from its parallel key of
But, your question is worded such that I think you ask: if chords borrowed in C major from C minor are used in C major's relative minor -
A minor - does their function change?
I think you can simply answer "yes" because when any given tone - example
G - is considered in two different keys its position in the scale changes and therefore its function changes. Again, with an example of
C major it is the dominant, but in
A minor it is the subtonic. That is a change of function. The change did not happen from altering the pitch! The function changed, because the tonic changed, and that changed the position of tones in the scales.
But, let's look at the borrowed chords and how they would be identified in the relative minor. Keep in mind that with chord label capital letters mean major, lower case mean minor, the 'o' means diminished, and a flat prefix means the chord root is chromatically altered.
C : I ii iii IV V vi viio I
borrowed Cm : i iio bIII iv v bVI bVII i
cm do Eb fm gm Ab Bb cm
rel minor Am: III iv v VI VII i iio III
C dm em F G am bo C
borrowed : Ab Bb cm do Eb fm gm (Ab Bb cm)
chords from bI bII iii ivo bV vi vii (bI bII iii)
I notice three things immediately.
- when the borrowed bVI (Ab) is placed in
A minor we chromatically alter the tonic!!! We have changed the key/mode and the whole premise of the question collapses.
- when the borrowed bIII (Eb) is placed in
A minor we chromatically alter the dominant!!! That's basically tonal self-destruction.
- When the put
bVII (Bb) and
v (gm) in
A minor we get chords that come from the parallel
A Phrygian mode. That's interesting, but it's much simpler to just think of borrowing chord from the parallel Phrygian than calling this 'borrowing chords from the relative major's parallel minor.'
I hope I didn't misunderstand your question.
The explanation is a bit convoluted.
But, the simple answer is: yes the chords will change.
I'm adding some detail specifically about borrowing chords in a minor key from the parallel major.
I think it is much more common that chords are borrowed in major keys from their parallel minors. In fact, the textbooks examples I can think of always shows borrowing in major from parallel minor. Be that as it may, let's continue looking at the idea of borrowing in minor from parallel major.
A caveat: my conception of major/minor harmony comes from the rule of the octave and figured bass. That is the old teaching which was used by Handel, Bach, Haydn, Mozart, etc. etc. It is not the teaching in modern harmony textbooks. I believe the difference in the two methods becomes pronounced when looking at minor harmony. I won't go into the details contrasting the two methods, but only say that what follow is my conception of harmony as based on the older teaching.
Now the chart...
The first problem to deal with is the notion that there is only one chord type per scale degree in minor. From the perspective of figured bass this simply is wrong. In figured bass/rule of the octave the chord types are determined by the direction of bass movement! For some - but not all - people using a modern approach they say the set of chords in minor is derived from the "harmonic" minor scale, or the ascending form of "melodic" minor, or the "natural" minor. Those approaches will yield a single set of chords per scale degree. If the ascending/descending melodic minor is used, it may generate a chord set like the rule of the octave, but not necessarily. I used the natural minor as the basic chord set, because those are the diatonic chords resulting from the modern minor key signature. Sorry for such a tedious explanation of the chord set, but it matters when explaining how I identify the 'source' of the chords.
Below the natural minor chords, I list the chords which would be "borrowed" from the parallel major. The natural sign is used to show when the chord root is altered in the borrowing. In actuality other accidentals could be used depending on the key signature.
Below the borrowed chords I indicate which scale degrees are altered from the natural minor to produce the chord borrowed from parallel major.
I boxed in yellow the chords altered in minor to either create proper dominant chords with a raised
^7 leading tone, or for cadential harmony like
IV6 V6 i. From the perspective of figured bass it is this harmonic reason that the
^7 scale degrees are altered.
Now let's examine each chord with my comments about its 'source:'
I(7) neither the rule of the octave nor any of the chord sets from various minor scales will raise
^3 and produce this chord, the only way to get it is either borrow it from major or its treatment as a secondary dominant of
iv. To make the secondary dominant possibility clearer I added the 7th in parenthesis, but in analysis it would really be labelled
ii the rule of the octave doesn't produce this chord, of course it will occur, but it wouldn't be a primary harmony, as a type of subdominant in minor it will typically use the lowered, unaltered
^6 degree, for this reason I say it would be borrowed from major.
♮iii in general the mediant triad is rare in the major/minor system, again the
^3 degree isn't normally altered and in this case the raised
^7 degree isn't involved with dominant harmony, it would appear as a chord borrowed from major.
IV is of course a primary triad and an important cadential chord, the rule of the octave uses this chord in minor only when the bass ascends through
V6, the harmonic minor scale won't produce it, so I give its source as the ascending melodic minor.
V this chord is produced by altering
^7 to make a leading tone and a true dominant chord, it's essential for cadences, at a minimum the harmonic minor will produce it so I gave that as the origin.
♮vi similar to
♮III this involves altering
^3 but the raised
^7 does not involve dominant harmony, the rule of the octave only alters
^7 for create dominant haromny, that isn't the case here, therefore its source would be borrowing from the parallel major
♮viio this chord is a kind of alternate
V involving the leading tone and dominant harmony coming from the harmonic minor scale.
So, my conclusion, based on my understanding of figured bass harmony is:
I IV V ♮viio while technically could be called chords borrowed from the parallel major are actually the result of alterations to produce cadential/dominant harmony, but chords
ii iii vi are not cadential/dominant harmonies and therefore borrowed from the parallel major.
A final thought: during the time of the figured bass all kinds of chromatic chords could be produced through the contrapuntal movement of voices. In that case the handling of altered tones become a linear property taking us away from the homophonic notion of chords/harmony. Bach's 371 Harmonized Chorales is my go-to source for finding just about any possible movement of voices/chords. In it I'm sure you can find examples like a minor key passage using a root position
ii chord. Call it borrowed if you like. But it probably will be more insightful in such a case to identify it in terms of linear scales and counterpoint. My chart above is meant to apply to a homophonic rather than contrapuntal style.