I have just read again the excellent compendium given by M. Cousin in his _General History of Philosophy from the most Ancient Times to the End of the Eighteenth Century_. He establishes that all the philosophical labours of the human understanding have terminated in four great systems--sensualism, idealism, scepticism, and mysticism--the sole actors in that intellectual arena where, in all ages and amongst all nations, they are in turn in the position of combatants and of sovereigns. {127} And, after having clearly characterised in their origin and their development these four systems, M. Cousin adds, "As for their intrinsic merits, habituate yourselves to this principle: they have existed; therefore they had their reason to exist; therefore they are true at least in part. Error is the law of our nature: to it we are condemned; and in all our opinions and all our words there is always a large allowance to be made for error, and too often for absurdity. But absolute absurdity does not enter into the mind of man; it is the excellence of man's thought, that without some leaven of truth it admits nothing, and absolute error is impossible. The four systems which have just been rapidly laid before you have had each their existence; therefore they contain truth, still without being entirely true. Partially true, and partially false, these systems reappear at all the great epochs. Time cannot destroy any one of them, nor can it beget any new one, because time develops and perfects the human mind, though without changing its nature and its fundamental tendencies. {128} Time does no more than multiply and vary almost infinitely the combinations of the four simple and elementary systems. Hence originate those countless systems which history collects and which it is its office to explain." [Footnote 24] [Footnote 24: Histoire Générale de la Philosophic depuis les temps les plus anciens jusqu'à la fin du XVIII Siècle, par M. Victor Cousin, pp. 4-31. 1863.]