ANNOTATING HARMONY FOR TRIAD CHORDS IN ROOT POSITION 

The next figure shows how to annotate harmony for triad chords in the root position. The C major key and the A minor key are used. Thus, the assumption is that the chords in the figure are taken from passages written in these keys. The chords shown in the figure are in the root close position but the same annotations are also used for open positions. 

Figure: Annotating harmony for triad chords in the root position

The C major triad chord is annotated in the C major key as C: I. The chord root C is the first scale degree of the C major key. Thus, it is annotated with the Roman numeral one. The interval between the chord root and chord third (C4 E4) is the major third. Thus, the Roman numeral is in the upper case.

The A minor triad chord is annotated in the C major key as C: vi. The chord root A is the sixth scale degree of the C major key. Thus, it is annotated with the Roman numeral six. The interval between the chord root and chord third (A4 C5) is the minor third. Thus, the Roman numeral is in the lower case.

The B diminished triad chord is annotated in the C major key as C: viio. The chord root B is the seventh scale degree of the C major key. Thus, it is annotated with the Roman numeral seven. The interval between the chord root and chord third (B4 D5) is the minor third. Thus, the Roman numeral is in the lower case.

The C augmented triad chord is annotated in the A minor key as a: III+. The chord root C is the third scale degree of the A minor key. Thus, it is annotated with the Roman numeral three. The interval between the chord root and chord third (C4 E4) is the major third. Thus, the Roman numeral is in the upper case.