form ever follows function

It is the pervading law of all things organic and inorganic, of all things physical and metaphysical, of all things human and all things superhuman, of all true manifestations of the head, of the heart, of the soul, that the life is recognizable in its expression, that form ever follows function. This is the law.

—Louis Sullivan, "The Tall Office Building Artistically Considered," Lippincott's Magazine (March 1896)