A convention for describing chords
Without getting bogged down with terminology, it’s going to be useful in this corner of the lab to describe chords in a generic fashion that works with any of the 12 possible major or minor keys. The commonly accepted way to do this is using Roman numerals.
Let’s take the key of C major as an example, which has a scale of C D E F G A B. If you build a triad on each note in the scale, using only notes in the scale, you get these seven chords (called tonic chords): C Dm Em F G Am Bdim. If you want to describe a progression that uses these chords but in a way that works for all major keys, you can use the following labels: I ii iii IV V vi viiº, where upper case Roman numerals represent major chords and lower case numerals represent minor chords. Diminished chords are shown in lower case followed by a degree sign and augmented chords in upper case followed by a plus sign.
The table that follows provides a summary and provides examples for both C major key and C minor.
| Scale degree | Tonic | Supertonic | Mediant | Subdominant | Dominant | Submediant | Leading tone |
| Chord symbols for major (minor) keys | I (i) | II (ii) | III (iii) | IV (iv) | V (v) | VI (vi) | VII (vii) |
| Example: C major (scale: C D E F G A B) | I (C) | ii (Dm) | iii (Em) | IV (F) | V (G) | vi (Am) | viiº (B dim) |
| Example: C minor (scale: C D Eb F G Ab Bb) | i (Cm) | iiº (D dim) | III (Eb) | iv (Fm) | v (Gm) | VI (Ab) | VII (Bb) |
So, the symbol V means a major chord at the Dominant scale degree (we won’t be referring to these labels again). In the key of C or Cm that would be G. In the key of E or Em that would be B. Similarly, the symbol ii means a minor chord at the Supertonic scale degree. In the key of C or Cm that would be Dm. In the key of E or Em that would be F#m.
Phew.