Harmony/Harmonic Function & Harmonic Progression

The Language of Harmony
Whilst explaining triads, we touched on the description of harmony. Harmony is often functional, with frequent chord changes to fit a melody. It is therefore essential to be able to describe harmony precisely and concisely.

Roman Numeral Component
In a given key, a chord can be described with a given Roman numeral. This is based on how far the root note of the chord is away from the tonic note of that key.

It is useful to denote chords I, IV, and V in capitals, and chords ii, iii, vi, vii in lowercase.

Added or Altered Notes
Extra notes on a chord, such as 7ths as already discussed, are written after this numeral as superscript (similar to indices in mathematics). An accidental can be placed by this note if that is needed.

Inversions
Inversions can also be described with a standard alphabet letter, although this will be covered in greater detail later on.


 * Root inversion = a (or nothing)
 * 1st inversion = b
 * 2nd inversion = c
 * 3rd inversion = d

Accidentals
If a chord is not what is expected based on the key (for example, a major chord in a minor key), the accidental is written underneath the Roman numeral. This is often called using a 'borrowed chord' or 'mode mixture'.

All of these descriptions can help us describe harmony in a way that relates each chord to the others based on the key signature.

Root Movement
The strongest movements (in terms of progression in terms of Roman numerals) are:


 * Down 5
 * Down 3
 * Up 2
 * (Down 4)

We will see later when we look at cadences that these root movements can help us explain why they sound strong.

Harmonic progression isn't just about getting chords in the correct order - it's also about making any part-writing sounds smooth. What this means is that when harmony is written down, it can often sound 'clunky' - over the years, composers have identified that parallelism is an effective way to smooth out harmonic progressions.

Parallelism
Parallelism is where two parts move in the same direction by the same interval at the same time.

Good Parallelism

 * 3rds
 * 6ths
 * 10ths

Bad Parallelism

 * 5ths
 * 8ths (except when doubling an important part)

Further Work
A good place to start when looking at writing for parts (and how to use parallelism to your advantage) is J.S. Bach's Harmonised Chorales, a set of Lutheran hymn tunes with SATB writing. With 371 to choose from, they are a comprehensive way to begin an understanding of part writing.

Bach Harmonised Chorales

To learn more about 'borrowed chords', have a look at this Wikipedia article.

Borrowed Chords