Harmony in 4ths - known as quartal harmony - was introduced in the early 20th century by European composers such as Ravel and Bartok, among others.
In the 1960s, its use was pioneered by American pianists, most notably McCoy Tyner and Herbie Hancock, and spread rapidly to improvisers on all melodic instruments.
In this post we'll take a look at an example of P4s in a melodic line over a familiar harmonic device - namely the iii-VI-ii-V-I chord sequence.