Nevertheless, it must indeed be owned, philosophy has not entirely lost, and sometimes still retains, since Descartes and in Descartes himself, its old habits. It rarely belongs to the same man to open and run a career, and usually the inventor succumbs under the weight of his own invention. So Descartes, after having so well placed the point of departure for all philosophical investigation, more than once forgets analysis, and returns, at least in form, to the ancient philosophy.[6] The true method, again, is more than once effaced in the hands of his first successors, under the always increasing influence of the mathematical method. Two periods may be distinguished in the Cartesian era,--one in which the method, in its newness, is often misconceived; the other, in which one is forced, at least, to re-enter the salutary way opened by Descartes. To the first belong Malebranche, Spinoza, Leibnitz himself; to the second, the philosophers of the eighteenth century. Without doubt Malebranche, upon some points, descended very far into interior investigation; but most of the time he gave himself up to wander in an imaginary world, and lost sight of the real world. It is not a method that is wanting to Spinoza, but a good method; his error consists in having applied to philosophy the geometrical method, which proceeds by axioms, definitions, theorems, corollaries; no one has made less use of the psychological method; that is the principle and the condemnation of his system. The _Nouveaux Essais sur l'Entendement Humain_ exhibit Leibnitz opposing observation to observation, analysis to analysis; but his genius usually hovers over science, instead of advancing in it step by step; hence the results at which he arrives are often only brilliant hypotheses, for example, the pre-established harmony, now relegated among the analogous hypotheses of occasional causes and a plastic mediator. In general, the philosophy of the seventeenth century, by not employing with sufficient rigor and firmness the method with which Descartes had armed it, produced little else than systems, ingenious without doubt, bold and profound, but often also rash,--systems that have failed to keep their place in science.[7] In fact, nothing is durable except that which is founded upon a sound method; time destroys all the rest; time, which re-collects, fecundates, aggrandizes the least germs of truth deposited in the humblest analyses, strikes without pity, engulfs hypotheses, even those of genius. Time takes a step, and arbitrary systems are overturned; the statues of their authors alone remain standing over their ruins. The task of the friend of truth is to search for the useful remains of them, that survive and can serve for new and more solid constructions.