Section 21.7 Descending Chromatic Bass Lines
A common musical pattern is the descending chromatic bass line (\(\hat{1} \)–\(\hat{7} \)–♭\(\hat{7} \)–\(\hat{6} \)–♭\(\hat{6} \)–\(\hat{5} \)). Composers harmonize descending chromatic bass lines with all manner of harmonies, including secondary chords, borrowed chords, augmented sixth chords, and rarely-used diatonic chords. Below are some examples from the past four centuries.
Below is a table comparing the harmonizations of these descending bass lines.
Bass Line | \(\hat{1} \) | \(\hat{7} \) | ♭\(\hat{7} \) | \(\hat{6} \) | ♭\(\hat{6} \) | \(\hat{5} \) |
Purcell | \(\left.\text{i}\right.\) | \(\left.\text{V}^{6}\right.\) | \(\left.\text{V}^{4}_{2}\middle/\text{iv}\right.\) | \(\left.\text{IV}^{6}\right.\) | \(\left.\text{iv}^{6}\right.\) | \(\left.\text{V}\right.\) |
Bach | \(\left.\text{i}\right.\)–\(\left.\text{vii}^{\circ}{}^{4}_{3}\middle/\text{V}\right.\) | \(\left.\text{V}^{6}\right.\) | \(\left.\text{vii}^{7}\right.\)–\(\left.\text{vii}^{\circ}{}^{4}_{3}\middle/\text{iv}\right.\) | \(\left.\text{IV}^{6}\right.\) | \(\left.\text{iv}^{6}\right.\)–\(\left.\text{Fr}^{+6}\right.\) | \(\left.\text{i}^{6}_{4}\right.\)–\(\left.\text{V}^{6}\right.\) |
Beethoven | \(\left.\text{i}\right.\) | \(\left.\text{V}^{6}\right.\) | \(\left.\text{V}^{4}_{2}\middle/\text{iv}\right.\) | \(\left.\text{IV}^{6}\right.\) | \(\left.\text{Ger}^{+6}\right.\) | \(\left.\text{i}^{6}_{4}\right.\) |
Beatles | \(\left.\text{i}\right.\) | \(\left.\text{i}^{4}_{2}\right.\) | \(\left.\text{IV}^{6}_{5}\right.\) | \(\left.\text{VI}\right.\) | ||
Led Zeppellin | \(\left.\text{i}\right.\) | \(\left.\text{III}\right.\)\(\left.\text{}^{+M}\right.\)\(\left.\text{}^{4}_{3}\right.\) | \(\left.\text{i}^{4}_{2}\right.\) | \(\left.\text{IV}^{6}\right.\) | \(\left.\text{VI}^{M7}\right.\) | |
Aerosmith | \(\left.\text{i}\right.\) | \(\left.\text{i}^{4}_{2}\right.\) | ♯\(\left.\text{vi}^ø{}^{7}\right.\) | \(\left.\text{VI}^{M7}\right.\) | ||
S.T.P. | \(\left.\text{i}\right.\) | \(\left.\text{V}^{6}\right.\) | \(\left.\text{V}^{4}_{2}\middle/\text{iv}\right.\) | ♯\(\left.\text{vi}^ø{}^{7}\right.\) | (\(\left.\text{VI}\right.\)) | |
Perri | \(\left.\text{i}\right.\) | \(\left.\text{V}^{6}\right.\) | \(\left.\text{i}^{4}_{2}\right.\) | \(\left.\text{IV}^{6}\right.\) |
For the harmonization of scale degree \(\hat{6} \), remember that the concept of ♯\(\left.\text{vi}^{\circ}{}\right.\) was introduced when Roman numerals in minor were introduced. The notes of the ♯\(\left.\text{vi}^ø{}^{7}\right.\) chord belong to the melodic minor scale.