 Spencer and Darwin expressed admiration for each other’s work, although Kivy (1959: 47) points out that they were also aware of their crucial methodological differences. While the former relied on general laws as ultimate explanatory principles, Darwin accepted generalizations only insofar as they were supported by empirical evidence. Exemplary of this contrast is one of Spencer’s arguments against the view that music develops out of vocalizations employed during courtship. Spencer holds that it is “one of the fundamental laws of evolution” that “[a]ll development proceeds from the general to the special” (1890: 458). To say that a subset of vocalizations (those used during courtship) has generated a more general class of sounds (all vocalizations expressing emotions, including music) is to contradict that principle.