7Q2 THE AMERICAN JOURNAL OF SOCIOLOGY
phases society, like an organism, follows a path predetermined and predictable.
The new school, on the other hand, emphasizes discontinuity. Far from being a smooth upward slope, the way of progress is a ladder with rungs at very unequal intervals. Group-life tends toward an equilibrium. Forms petrify rather than pass into something else. An impulse spends itself, and society, with no new push, comes to rest. The causes of change are, then, to be sought, not in society, but in impinging sub-social or extra-social forces stimuli, so to speak. Conquest, the intrusion of an alien race, migration to a new seat, are apt to play havoc with the curves plotted by the development theorist. If the disturbing factor does not intrude from without, it pushes up from below. The genius is not a social but a vital phenomenon. Inventions and discoveries break in from what Professor James terms "the physiological cycle." Social destiny pivots on the advent of a brain that can invent gunpowder, the watermill, the compass, the printing-press, the locomotive in a word, on individual causes. At every instant a people has a number of paths open to it, and which one it will follow depends on those physiological variations which produce genius. The only paths the sociologist may plot are those by which an invention radiates from the inventor and becomes generalized. The only dynamic laws are laws of imitations, interferences, and adaptations.
Now, each of these views, the old and the new, reveals a part of the truth, and, in the judgment of the writer, the time has come to broaden social dynamics until it includes them both. Let us first consider just how society may be modified by the operations of resident forces.
Among the causes of social change may be distinguished two sorts of alteration qualitative and quantitative. A mechanical invention, a scientic discovery, a new conception of life, a crossing of races, exemplifies the former. An increase or decrease of resources, or capital, orof somecomponent of the population, exem- plifies the latter. Thus the softening of slavery into serfdom may follow the promulgation of a new dogma or a growing scarcity of slaves. A new theory of races may make a slave code
