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The Elements of Harmony > Chords (in-depth)

Chord Flow

The idea behind all Western music is to create tension and release through the alternation of Tonic
function (I, iii, vi) and Dominant function (V, vii) chords. Triads or Quadriads built on degrees V and VII
contain the scale note (the "leading tone") one half-step below the root of the Tonic chord I
[see Chords (basic)], and therefore set up the highest possible degree of tension with I.

The iii chord also contains the leading tone, but is best considered as a V chord with a suspended 6^th
which then resolves down to form a full V chord.

The IV chord contains a note one half-step above the 3^rd of I, but also contain the root of I. For this
reason the tension it creates with I is not as great as that of the Dominant function chords. As an alternative
to resolving IV to I (called a "plagal cadence"), we may chose to increase the tension further, by changing
the notes of IV to those of V, and then follow with a strong resolution to I (called a "perfect cadence").

Harmonic progressions are composed by stringing together chord functions while giving a balanced sense
of tension-release. The Chord Flow Chart below shows the available directions at each step of the way.
Almost all routes are open at any junction, except:

ii IV/iv and vi/VI I which provide too weak a release in tension.

ii I which is almost impossible to resolve without creating similar motion in the voice leading (similar

motion should always be avoided in good counterpoint).

V ii which is impossible since the leading note must rise to the Tonic.

ii vi and IV vi which would sound like a modulation to vi.

ii VI would present difficulties since any note forming a diminished 5^th must descend.

Note that the chords for some functions can be major or minor, depending on the prevailing key.

Note also that the height of the boxes above the Tonic box represent the degree of tension away from

the Tonic.