Describe the function of the tritone substitution and how it can be used to create harmonic tension and resolution in a ii-V-I progression.

The tritone substitution is a fundamental technique in jazz harmony, where the dominant 7th chord (V7) in a progression is replaced by another dominant 7th chord that is a tritone away. The tritone is an interval of six half steps, or three whole steps, and in the context of a dominant 7th chord, this interval exists between the 3rd and 7th notes of the chord. The most common tritone substitution is the flat-five substitute, which is often referred to as bII7. For example, if the dominant chord is G7, its tritone substitution would be Db7. The function of the tritone substitution lies in its ability to maintain the dominant function of the V7 chord while altering its sound, creating harmonic interest and a sense of surprise. This works because both chords share the same tritone interval between their 3rd and 7th, the critical interval that creates the dominant function by resolving inwards to the root and third of the tonic chord. In a typical ii-V-I progression, the tritone substitution of the V7 chord can dramatically change the harmonic landscape. Let's take a ii-V-I in the key of C ma....