It appears that many people who come to this blog are looking for help with theory homework. I'll try to put up the occasional post that offers some suggestions and tricks that I've taught (and used!) over the years.
In this first installment, we'll tackle root-position partwriting. Most of what you see here is distilled from the Kostka-Payne textbook, Tonal harmony, which we used here at Texas Tech for a number of years. The rules below apply to diatonic chords only; they require some adaptation for chromatic harmony.
There are basically three ways any two triads can be related:
If two chords have roots that are a fourth or fifth apart, they will have one tone in common. For example, a C-major triad is spelled C-E-G, and a G-major triad is spelled G-B-D. The fifth of the C-major triad (G) is the same as the root of the G-major triad. When partwriting with triads whose roots are a fifth apart, you should try to retain the common tone from chord to chord. Move the upper voices to the nearest available chord member.
NB. In all of these cases try to move the upper voices in contrary motion to the bass. If the bass moves up, move the upper voices down. If the bass moves down, move the upper voices up.
If two chords have roots that are a third or sixth apart, they will have two common tones. Compare C major with E minor: C major is spelled C-E-G; E minor is spelled E-G-B. The two triads have E and G in common. Try to keep these two notes in common and move the other voices in contrary motion to the bass to the next available chord member.
If two chords have roots that are a second or a seventh apart, they will have no pitches in common. A C-major triad is spelled C-E-G; a D-minor triad is spelled D-F-A. In this situation, move the upper voices in contrary motion to the bass to the next available chord member. This way, you'll avoid parallel fifths.
In this first installment, we'll tackle root-position partwriting. Most of what you see here is distilled from the Kostka-Payne textbook, Tonal harmony, which we used here at Texas Tech for a number of years. The rules below apply to diatonic chords only; they require some adaptation for chromatic harmony.
There are basically three ways any two triads can be related:
- Their roots could be a fourth or fifth apart (ex. C major and G major; A minor and E minor)
- Their roots could be a third or sixth apart (ex. C major and E minor; A minor and C major)
- Their roots could be a second or a seventh apart (ex. C major and D minor; E minor and F major)
If two chords have roots that are a fourth or fifth apart, they will have one tone in common. For example, a C-major triad is spelled C-E-G, and a G-major triad is spelled G-B-D. The fifth of the C-major triad (G) is the same as the root of the G-major triad. When partwriting with triads whose roots are a fifth apart, you should try to retain the common tone from chord to chord. Move the upper voices to the nearest available chord member.
NB. In all of these cases try to move the upper voices in contrary motion to the bass. If the bass moves up, move the upper voices down. If the bass moves down, move the upper voices up.
If two chords have roots that are a third or sixth apart, they will have two common tones. Compare C major with E minor: C major is spelled C-E-G; E minor is spelled E-G-B. The two triads have E and G in common. Try to keep these two notes in common and move the other voices in contrary motion to the bass to the next available chord member.
If two chords have roots that are a second or a seventh apart, they will have no pitches in common. A C-major triad is spelled C-E-G; a D-minor triad is spelled D-F-A. In this situation, move the upper voices in contrary motion to the bass to the next available chord member. This way, you'll avoid parallel fifths.