Disclaimer: this paper is a personal view on two- part writing way off the academic approach.
Two simultaneous notes form an interval while a greater number of simultaneous notes creates either chords or other terms such as Cluster that depend on school and music eras.
In a nutshell, counterpoint uses interval while harmony is based on chords; so Two-part writing is logically the concern of counterpoint.However,counterpoint is prior to tonal music and its rules, justified by Pythagorean intervals, are somehow obsolete with equal temperament. In an other hand, tonal harmony stems from counterpoint and therefore shares some rules with it but its at least three voices setting induces inaccuracy in two-part writing. That might be the reason of the scattered number of published methods
Hindemith is one of the most prominent contributors to tonal renewal of counterpoint but his sophisticated method might be hard to start with.
This paper is an attempt to draw some functional implications of intervals from tonal considerations .
Tonal music consists of two modes: the Major mode and the minor mode which can appear under three aspects :
-The natural scale or descending melodic scale similar to eolian mode with a subtonic instead of leading tone.
-The harmonic minor scale ;a leading tone replace the subtonic.
-The ascending melodic scale with a sharped sixth degree to correct the augmented interval created by the leading tone.
Stacks of thirds over each scales degrees yield four kinds of triads
- Major triad made of a Major third and a minor third (from bottom to top)
- Minor triad formed by a minor third and a major third
- diminished fifth triad that consist of two minor thirds (to differentiate from consonant harmony)
- Augmented fifth triad made of two major thirds (which does not belong to tonal harmony)
Scale degrees are not equal in importance
The most important are I-IV-V known as primary or tonal chords which support either a major or a minor triad according to the mode.
others chords are secondary chords that may be of any kind according to the scale.
4°) Chord inversion.
Any triad has two inversions but some are uncommon . As a rule, only primary chords can non-restrictively be inverted. II and VII can be inverted under some conditions.Other chords are normally not inverted but in sequence
Inversions result in chord structure changes.
When an incomplete chord is needed the fifth is generally omitted. Therefore, chords in root position appear under a third form (either Major or minor).
The third is obviously omitted in diminished fifth chord.
In tonal harmony the third can be omitted
-in the Dominant chord and the Tonic chord if the key is well established. Thus, a perfect fifth means V or I
–in sixth chords so first inverted chords are under the form of a Sixth interval
The fourth can be omitted in 4/6 cadential chord or the passing VII (b) on a weak beat
Removal of the sixth may occur in I6 ,V6 and VII4/6 which occur under a minor third structure
3 means either 5/3 or 6/3. Thus, CE can CEG or CEA
6 is 6/3 or 6/4. EC can be EGC or EAC
Primary chords prevails when interpreting an Interval .Therefore, with CE in CM we choose CEG=I5 but in minor we’d choose CEA=I6
The precedence is
I >VI>III so EG is I6 ,not III5 (In CM)
V>III GE is I4/6,not III5
but IV is equal II
From all those considerations we can establish the following guideline
7°) Rhythmic position
is the last consideration to take into account: Especially secondary chords should be on weak beat.
Although the logic is different from the classical taught counterpoint, usage shows a similar result with the classical writing rules so Much ado about nothing but I did try.