If I write in c minor, is c the VI or the I? Also what about Dominant, tonic and that stuff, are they the same as in Eb major? Otherwise I could only write deceptive cadences in minor keys if I end on c minor, correct?
In c minor, the diatonic triads are:
- i (c minor)
- ii° (d diminished)
- III (E♭ major)
- iv (f minor)
- v (g minor) or V (G major, if you use harmonic or melodic minor)
- VI (A♭ major)
- VII (B♭ major)
- vii° (b diminished, if you use harmonic or melodic minor).
That of course doesn't mean that these are the only ones you can use; for example you can modulate, use modal mixture (e.g. use a major IV in a minor key), use secondary dominants, etc.
While relative keys may share the same key signature (contain the same tones), they operate as independent systems. Each has its own Tonic, or key tone, that acts as the “home” note for the key.
Likewise, each related key has its own Roman numeral chord analysis. As relative keys, you’ll notice that the scale tones and the quality of the scalar chords built from those tones are identical (derivatives of each other). The main difference is the Tonic — the key tone acting as the gravitational center of the key.
So, in the key of C natural minor, C is the first degree of the scale (Tonic), G is the fifth degree (Dominant), and so forth.