 In “Progress, its Law and Cause,” Spencer makes a different argument.  He defines progress as “an advance from homogeneity of structure to heterogeneity of structure” (1857, v. 1, 9).  Progress occurs by way of “successive differentiations” (10).  The law of progress is simply that “every active force produces more than one change—every cause produces more than one effect” (37).  Spencer claims that all phenomena exhibit the same development from the simple to the complex for this same reason.  He finds evidence for progress in astronomy (10–11), geology (12–13), and linguistics (23–4). 