Composing a song in Cm with major chord substitutes

Question

I am composing a song in Cm with a very basic chord progression of I-IV-I. So, normally, in Cm, that would be Cm7-Fm7-Cm7, but I am actually playing Cm7-F7-Cm7.

First of all, why does this work? This mix & match of Major and Minor chords in a minor key. Secondly, the obvious transition from IV is to V (G7), and it's ok...but what other transitions could I go for? Maybe modulation to another key?

Answer 1

F7 Cm7 forms a weak cadence similar to that of F7 CM7: its guide tones resolve from a tritone to a perfect fourth and its root movement is a perfect fourth.

Depending on other factors, this song is likely to end up in Bb Major (where Cm7 and F7 form the II and V) or C Dorian (the related mode, somewhat less likely given the resolving tendencies of F7). Chords from these or related keys such as G Minor (relative minor) or Bb Minor (parallel minor) might be borrowed to good effect.

Answer 2

Firstly, you do not need to stay in a key for a chord sequence to 'work'. There is only one real rule in music and that is "If it sounds good, it is good." Many composers do not think in roman numerals, or about keys and come up with great music as a result.

However, this is not to say that you shouldn't. If thinking in keys works for you, then great. Just don't let it stifle what you do. I have no idea what you listen to, so it's hard to give a reference of a song that breaks the 'rules' and is still great but I'll go with Creep by Radiohead as an easy example. The sequence actually goes from a Bmaj to Bmin. Obviously these chords are not in the same key but it still works in the context they play it in. It's all about context.

I should also add if you do want to think of this sequence in terms of keys, you could say that the song is not in fact in Cm at all. It all depends on the "implied harmony" of the piece, which is to do with everything else that is going on, including rhythm, but I would say the piece is probably either in Bb Major (making Cm a II and F7 a V), or possibly Bb's relative minor, D Minor (making Cm a VII and F7 a III).

Hope this helps.

Answer 3

In the key of C minor, the chord built on the fourth degree would typically be an F minor chord. In the key of C major the chord built on the fourth scale degree would typically be F major. If one uses the F major chord in the key of C minor, this could be considered a "borrowed chord." Borrowed chords are taken from related keys and used in the tonic key (related keys to C minor would be C major, the parallel major; F minor, the subdominant; G major or minor, the dominant key; etc.)

Another solution for "why this works" is the potential use of a melodic minor scale. The melodic minor scale, going up, raise both the 6th and 7th scale degrees by half step (descending these scale degrees are played as in a natural minor scale). With these raised pitches, F and G would be major.

As far as the latter part of your question is concerned, there are almost limitless answers. If you are interested in different types of chords and progressions, I would suggest buying a music theory guide (I use Peter Spencer's Practice of Harmony).