by way of About Last Night:
"Music, as long as it exists, will always take its departure from the major triad and return to it. The musician cannot escape it any more than the painter his primary colors, or the architect his three dimensions. In composition, the triad or its direct extensions can never be avoided for more than a short time without completely confusing the listener. If the whim of an architect should produce a building in which all those parts which are normally vertical and horizontal (the floors, the walls and the ceilings) were at an oblique angle, a visitor would not tarry long in this perhaps 'interesting' but useless structure. It is the force of gravity, and no will of ours, that makes us adjust ourselves horizontally and vertically. In the world of tones, the triad corresponds to the force of gravity. It serves as our constant guiding point, our unit of measure, even in those sections of compositions which avoid it."
Paul Hindemith, The Craft of Musical Composition (1937, trans. Arthur Mendel)