CHAPTER 3 - THE BASIC HARMONIC SYSTEM

The chapter describes the most frequent and basic chord progressions in tonal music. It also shows the technique for applying these progressions to the harmonisation of the melody.

1. DESCRIPTION

- We refer to the Basic Harmonic System as the most elementary order that chord progressions tend to follow in classical tonal music.

- This order can be represented by the following scheme:

- As you can see, we make a distinction between two types of chords: Main chords and Substitutes. First of all, let's see how the Main Chords are used:

- The chords follow one after the other (  I - IV - V - I  ) in the order of the arrows.

- As the dotted arrow indicates, it is common to omit the Subdominant, which would result in I - V - I.

- Chord progressions in classical tonal music can be considered as constantly "circling" around this scheme. Thus, the I at the end of one turn becomes the initial I of the next:

2. SUBSTITUTE CHORDS

- If only the main chords were used, harmonisation would become repetitive and boring. Substitute chords allow the introduction of new formulas and therefore variety and interest from a harmonic point of view.

- Substitute chords are often used in two ways:

1. Substitution: as the name suggests, the substitute chord can replace the main chord. Examples:

I - II - V - I

I - IV - V - VI

VI - II - V - I

I - V - VI

2. Expansion: substitute chords are also applied to expand the Tonic or Subdominant function by 2 chords, placing the substitute after the main chord. Examples:

[ I - VI ] - IV - V - I

I - [ IV - II ] - V - I

[ I - VI ] - [ IV - II ] - V - I

- The substitute chord can also be placed before the main chord, although this happens less frequently (this is why this situation is represented by a dashed arrow in the diagram of the of the B.H.S.):

I - [ II - IV ] - V - I

3. BEGINNING AND END OF A PIECE ( OR EXERCISE )

- Normally, pieces within classical tonal music, and therefore also our exercises, begin with I and also end with I.

- Exceptionally, at the beginning of a piece or section, or at the end of the piece, the Dominant is omitted. The result is thus the progression I - IV - I.

- Strangely enough, this formula does not usually use substitute chords. That is to say, if we apply it, we would only use the progression I - IV - I.

4. HARMONIZING THE MELODY OF A HARMONIC STRUCTURE

- We call "Harmonising a Melody" of a Harmonic Structure to adding the 3 lower voices, Alto, Tenor and Bass to the melody, which is the Soprano. To do this we will follow several steps:

STEP 1: Choosing the chords. We do this for the entire melody, studying which formulas of the B.H.S. adapt to it, and selecting the ones we consider appropriate. Important: we will not repeat the same chord on 2 consecutive notes.

Im. 3.4a

STEP 2: In blocks of a few chords (5, 6, ...) we propose a Bassline.

Im. 3.4b

STEP 3: Once that fragment of the bassline is written, we write the inner voices.

Im. 3.4c

- If we find that the realisation is difficult, or even impossible, we will have to go back and come up with a different bassline. Or choose different chords (sometimes there is even no choice but to erase an entire previous fragment and find another way).

- On the other hand, if we write our block successfully, we can continue with the next block, following the same procedure, until the whole structure is completed.

Im. 3.4d

5. SUGGESTED EXERCISES

- Write, for the following melodies (sung by the Soprano), the 3 lower voices, taking into account the indications explained in this chapter.