Sometimes you may have only a bass line given as a suggestion for a four or three voice harmonization. Since we are using root position chords only, the implication is that each bass note is the root of a chord. Following these basic steps will reduce the difficulty of the task.
1. Determine the key
Remember, the key signature
alone cannot reveal the key of a piece. Each key signature has two
possibilties; major and the relative minor. You might
glance at the end
of the piece for a hint. Phrases tend to end on the tonic or dominant
chord. Another hint could be the frequency of the tonic or
dominant notes throughout
the phrase. Also look for the leading tone in the minor key.
2. Write an harmonic analysis. Once you have ascertained the key of the piece, place the name of the key and all of the Roman numerals below the bass notes.
3. Add 2 voices or add 3 voices using rules for chord connections
If you add soprano, alto,
and tenor to the bass line, be sure to follow the correct procedures for
connecting root position chords in 4 voices. If you are
only adding 2 voices to
the bass line, move the voices cautiously being careful not to write any
parallel fifths or octaves. Also be sure that each chord has
a third present.
4. Strive for contrary motion between bass and soprano
Since we are intent on having
independence between the separate vocal lines, it is advisable to try to
have your soprano going in opposite direction
to the bass. Do
not force this concept. Similar and oblique motion are often
equally good between the soprano and bass. Always keep in mind
that the lines you add are
expected to be good melodies. That is more important than
any of the movements between voices.
5. Figured bass symbols
Following the procedures outlined above, we would first determine the key. Two flats could be either Bb major or G minor. There are lots of G's and D's (the tonic and dominant of G minor) and no Bb's or F's (tonic and dominant of Bb major). Furthermore, the accidental which reappears often under the D's affects the note that is a third above the D. This sharp tells us that there is an F# in the chord. This F# virtually destroys any possibility of the key being Bb major, since F natural is the second most important note in that key. Also you may recognize the F# as the leading tone in the key of G minor. Once we know the key, it is a simple matter to label each chord. The first chord is G minor (G - Bb - D). In the key of G minor, this is a i chord. So we place the i under the G. Following this procedure would result in this analysis.
If you still have questions, contact Dr. Bartolotta
at wbartolo@odu.edu