Fourth complement

The fourth complement of a given interval is its interval distance from the fourth (4/3). It's very similar to the fifth complement. It seems to be very useful in regards to tetrachords, and even in describing certain relationships in the functional harmony of Western Classical Music such as "parallels" in which notes in the same tetrachord located a third apart from each other share some aspects of their harmonic function.

History

Aside from the usage of the term "fourth complement" this wiki, the term was brought up by Aura in a discussion on Discord concerning reasons that the relationships between Perfect and Augmented Fourths is not entirely analogous to the relationship between major and minor seconds in MOSes despite being separated by the same interval.

Examples

The following interval pairs are fourth complementary to each other

• 5/4 and 16/15
• 6/5 and 10/9
• 8/7 and 7/6

See also

• Octave complement
• Fifth complement