Encyclopaedia Britannica, 11th Edition, "Coucy-le-Château" to "Crocodile"

part is concerned, as those in double counterpoint. Triple counterpoint

(and a fortiori multiple counterpoint) is normally possible only at the octave; for it will be found that if three parts are designed to invert in some other interval this will involve two of them inverting in a third interval which will give rise to incalculable difficulty. This makes the fourth of Brahms'...