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Home | Music Theory | Harmony

Music Theory - Harmony

Harmony is the study of chords. More specifically it is the study of the relationship between chords and scales. While music can consist solely of a melody line or percussive pattern, an accompanying harmony part will make it richer and more absorbing. Western music is dominated by the Diatonic Major Scale and so if we use this scale as a reference point we can establish rules and formulae that can be used as a basis for creating harmony.

The formula that generally underlies chord progressions is the harmonized major scale. Although there are exceptions they too can often be related back to this scale in some way.

Using the key of C major we can create a harmonised major scale by building a triad off of each note of the scale using only notes found within the scale:

I C-E-G 1-3-5 Cmaj
ii D-F-A 1-b3-5 Dmin
iii E-G-B 1-b3-5 Emin
IV F-A-C 1-3-5 Fmaj
V G-B-D 1-3-5 Gmaj
vi A-C-E 1-b3-5 Amin
vii B-D-F 1-b3-b5 Bdim
VIII C-E-G 1-3-5 Cmaj

Each of these triads is taken right out of the C major scale, but we could have used any major scale. C major is convenient simply because it contains no sharps.

By referring to the Roman numerals, we can talk about chord progressions without having to identify the key. For example, a very common chord progression is I-IV-V-I. I-IV-V-I means to play the chord built off of the first degree (note) of the scale followed by the chord built from the 4th degree, the chord built off of the 5th degree and back to the chord built off of the 1st degree. In the key of C, that would be C-F-G-C.

To play the progression in another key, you need to know the harmonised major scale for the key you want to play in. There is a formula to help you here, however. If you work out the harmonised major scale for any given key you will find that you get the same TYPES of chords in the EXACT SAME ORDER as before. The only thing that changes is the root note of each chord and the scale that the other notes in each chord follow. No matter what key we choose, the chord types will occur in the exact same order so long as we follow the major scale in that key. So all you have to learn is which number equates to which chord type and how far apart the chords are from one another.

The major scale follows this whole-step/half-step pattern:

w - w - h - w - w - w - h

The harmonised scale follows the same pattern:

I ii iii IV V vi vii VIII
w w h w w w h

Now, all you have to do is remember which type of chord each number represents.

I ii iii IV V vi vii VIII
w w h w w w h
maj min min maj maj min dim maj

Notice that upper case numerals are used for major chords and lower case for minor and diminished.

There is an old system for naming each chord within the scale:

I Tonic
ii Supertonic
iii Mediant
IV Subdominant
V Dominant
vi Submediant
vii Leading Tone

You will here the word "dominant" thrown around quite often. The others you may never run into, but you never know.

I

Harmony Type: Tonic
Scale Degrees Supported: 1 - 3 - 5
Major Version: Major
Minor Version: Minor
Can Lead To: Any chord type.
Rules:
The second inversion is not really used as a tonic chord, mostly used in the cadential 64.
The first inversion is good for expanding the tonic harmony as well as expansion of the supertonic chord.

II

Harmony Type: Pre-Dominant
Scale Degrees Supported: 2 - 4 - 6
Major Version: Minor
Minor Version: Diminished
Can Lead To: Dominant and other pre-dominant chords.
Rules:
ii is the V of V and therefore intensifies the authentic cadence ii-V-I.
In minor the root position is rarely used, because of its diminished quality, precautions must be used if this
inversion is used.
First inversion ii chords can freely substitute for root inversion IV chords.

III

Harmony Type: Secondary Dominant
Scale Degrees Supported: 3 - 5 - 7
Major Version: Minor
Minor Version: Major
Can Lead To: VI mostly, other cases can apply.
Rules:
In minor the major version is always used and is usually used the I-III-Vprogression, III being the mediant between I and V.
III in minor is its relative major, therefore care must be taken when dealing with this chord for it can easily slip into the relative major key.
The 5th of the chord should never be doubled, seventh scale degree.

IV

Harmony Type: Pre-Dominant
Scale Degrees Supported: 4 - 6 - 8
Major Version: Major
Minor Version: Minor
Can Lead To: Dominant and other pre-dominant. In some situations it can lead to tonic.
Rules:
IV-I is a plagel cadence.
First inversion IV chords can freely substitute for root inversion VI chords. IV6-V in minor only is a phrygian cadence.
IV6 can be also substitute for VI in deceptive cadences.

V

Harmony Type: Dominant
Scale Degrees Supported: 5 - 7 - 2
Major Version: Major
Minor Version: Major
Can Lead To: Tonic.
Rules:
the 3rd of the chord, seventh scale degree, should never be doubled.
V-I is an authentic cadence.

VI

Harmony Type: Pre-Dominant
Scale Degrees Supported: 6 - 1 - 3
Major Version: Minor
Minor Version: Major or Diminished
Can Lead To: Dominant and other pre-dominant chords.
Rules:
VI in major is the relative minor.
VI can freely substitute for I, usually with the 3rd of the chord doubled.
V-VI is a deceptive cadence.

VI

Harmony Type: Secondary Dominant
Scale Degrees Supported: 7 - 2 - 4
Major Version: Diminished
Minor Version: Major
Can Lead To: III mostly, other cases can apply.
Rules:
In major the root position is rarely used do to its diminished qualityand precautions must be used if it is used in root position.
Never double the root of VII chords.
VII in minor usually leads to III, VII being the V/III.
In major the viio6 can be used to expand the tonic chord.

Progressions

All chord progressions used during the common practice period follow the hierarchical system.

Tonic Dominant Pre-Dominant Secondary Dominants

Aside from these movements the composer must also look for the motion of thirds and fifths as the primary movement, these usually proceed as descending root progressions. Pre-dominant chords are used for preparing the dominant. Secondary dominants are not as commonly used as the others in harmonic progressions. The secondary dominants are mostly used in linear progressions and as applied dominants. Exceptions are made only when chords are used as filler. i.e. they are used in sequences and series or used as passing chords. Basic harmonic progressions are fifths, thirds, seconds in order of importance.





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