Simple as this consideration is, it has been too much neglected by historians and philosophers in recent times on account of the profound influence of the doctrine of evolution. The great service, which that doctrine has rendered, has been to fix our attention on the evident fact of continuity from which our minds had been distracted by a too exclusive preoccupation with theories of the atomic kind. Through several centuries, philosophy had acquired the habit of thinking generally in terms of elements and their compounds, whenever it addressed itself to a consideration of nature, or of the mind, or of the relation between the two. Its principal problem was to discover means of connection and unification which might make clear how that which is essentially discrete and discontinuous might, none the less, be combined into a unity of some sort. As it failed, it usually took refuge in the opposite idea, and attempted to conceive an original unity out of which diversity was generated by some impulsion in this initial and primal being. Philosophy thus vibrated between the contrasted poles of the same fundamental endeavor, between the attempt to combine elements into a unity, and the attempt to resolve unity into elements. The latter attempt, especially in men like Hegel and Spencer, had the advantage of involving the idea of continuity, and became the controlling philosophical enterprise of the latter part of the last century. But it was principally the doctrine of evolution or development as set forth by biologists, anthropologists, and historians that made the fact of continuity convincingly apparent and freed philosophy from the necessity of attempting to explain it. Continuity became a fact to be appreciated and understood, and ceased to be a riddle to be solved. The doctrine of evolution thus wrought a real emancipation of the mind.