>Step by step
Understanding and using basic tonal harmony
1 Mostly, Western tonal music is written either in a major or minor key. I’ll start by looking at major keys. Let’s start with a C major scale – eight notes from C to C, played on the white notes of the piano keyboard, to keep things simple for a moment – C D E F G A B C. The pattern of intervals between the notes in this scale is what gives it its major quality.
2 Here, we’ve harmonised the scale by stacking thirds up on top of each scale degree. This results in a set of diatonic chords – C, Dm, Em, F, G, Am, Bdim and C. The notes in each of the chords are taken from the parent scale of the key we’re in. Since this scale is C major, that makes these chords diatonic to the key of C major.
3 We can label these triads with Roman numerals, from 1 to 8, so that we can describe chord progressions without worrying about being in any particular key. Uppercase numerals are used for major chords, and lowercase for minor and diminished chords. So that gives us I, ii, iii, IV, V, vi, viiº and I, as shown here.
4 In tonal music, the way a chord works within the context of a musical key or harmonic progression (sequence of chords) is known as its harmonic function. Each chord in a progression will be there to perform a specific function, like setting up the next chord or increasing a feeling of instability. There are three kinds of harmonic function: tonic, predominant or dominant.
5 So, in tonal harmony, every chord in a diatonic set has a specific harmonic function. For instance, the ii and IV chords have a predominant function, meaning that they create a bit of tension, but not much. Their main purpose is to get you to the dominant chord in a progression. As an example, here’s a IV - V progression in the key of C major: F major - G major.
6 In contrast, the V and vii chords have a dominant function, meaning that they create a lot more tension. The main function of a dominant chord is to get you from a predominant chord to a tonic chord. In the key of C major, the V chord is G major, which really has a sense of wanting to go back to the tonic chord, C major.
7 The I, iii and vi chords have a tonic function, which essentially means that they have no tension at all, but are used to resolve the tension from the other chords. It’s easy to see how the well-known ii-V-I progression, used so much in jazz, came about – it follows the order predominant, dominant, tonic, or in C major, D minor - G major - C major, as shown here.
8 So tonal chord progressions are made up of chords whose function it is to drive the progression along towards the tonal centre, or tonic. To show how one chord’s function changes according to the key we’re in, a C major triad will have the tonic function in the key of C major, the predominant function in G major, and the dominant function in F major.
9 Let’s now look at minor tonality with a piece in C minor. The diatonic chords Eb, Ab, Bb for this key are Cm, Ddim, Fm, Gm, and Cm – all chords built from the C minor
Eb Ab Bb scale (C D FG C). The harmonic function is unchanged regardless of the major/minor make-up - i, III and VI are tonic, iiº and iv are predominant, and v and VII are dominant.
10 Our example piece consists of some drums, a synth bass part and a synth melody playing notes from the C minor scale. We’ll harmonise the melody by choosing chords from the diatonic set.
Bb Since the bass is just playing C and notes, this should fit nicely with our diatonic chords, so let’s go for the tonic as Eb- the first chord, C minor ( G-C).
11 We want a four-bar sequence to wrap around to Cm again, so after two bars of Cm, we’ll pick a predominant chord to go in bar 3. The iv chord of the key of Ab- C minor, Fm ( F- C), fits the bill nicely. This would logically be followed by a dominant Bb- chord in bar 4, so we’ll use Gm ( G- D), the v chord of C minor.
12 As the sequence rolls around to bar five, the recurring Cm chord resolves the tension provided by the Gm’s dominant function. And this time round, we’ll make a slight change - we keep the two bars of Cm in bars 5 and 6, and repeat the Fm in bar 7, but introduce a new final Bb Bbdominant chord in bar 8, ( F- D) - the VII chord in the key of C minor.