There's a question asking me about to identify mode borrowing, how do I do it? What is mode borrowing, may i have some examples?
'Borrowing' is a method of justifying a chromatic alteration - e.g. a Fm chord in a piece nominally in C major - by pointing out that though not diatonic in C major, it IS diatonic in C minor. Or we can 'borrow' from another mode rooted on C. D7 could be described as borrowed from C Lydian.
I generally find it more useful to consider the Fm as simply a chromatic alteration, D7 as V7 of V. But if you want to embrace 'borrowing', that's what it is.
"Mode borrowing" (also known under various different terms depending on whom you ask, see the Wikipedia page for a representative sample) refers to the specific instance of borrowing a chord from the parallel key, i.e. the tonality based on the same pitch, but in the opposite mode (major instead of minor, or vice-versa).
Typically, in Western music theory, any note (pitch) is most commonly associated with two modes, respectively, one built around the major and the other built around the minor scale which have the note in question as the starting point. One can build chords which fit with the given tonality by stacking thirds on top of each note of the scale (usually, one forms these chords by stacking 2 thirds on top of the given note, though this is not a hard limit - a very frequent example is the dominant seventh chord, formed by stacking 3 thirds on top of the 5th note of the scale, the "dominant"). For example:
Now, when writing a piece in, say, C minor, you would usually stick with the chords that belong to C minor (note: for simplicity's sake not included in either the simple scales above or in the example, but in the minor mode this also usually includes chords built on the raised sixth and seventh scale degrees [corresponding to the melodic minor scale]), for example:
However, nothing prevents you from spicing up the harmony of your piece in C minor a little bit by taking ("borrowing") chords from C major. A particularly common example is the "Picardy third", where at the end of a piece in the minor mode the final chord will be borrowed from the major. This can also be done with other chords (and need not be solely at the end of a piece, though I have stuck with that in the example for simplicity). This should be clear enough:
This is not the same thing as borrowing a chord from another key (seen most often in the function of a secondary dominant)!
Pretty straightforward, really. It's a way of explaining what happens in some pieces.
The tonic is stable - stays the same, and the mode, or key changes with regard to that tonic, or root.
So, taking a piece in, say, C major, the borrowing occurs when the notes in that piece go from those found diatonically in C major to those found in C minor. Quite a different set of notes!
Modal interchange is the same concept. Root C. C Dorian uses the notes from its parent key B♭. C Phrygian takes its notes from parent key A♭. C Mixolydian takes its notes from parent key G, etc. So any of these new 'keys' can be used to develop a piece that started in key C, as C is the common tonic.