When two persons meet together to discuss some enterprise or future event, or other speculative matter, without coming to an agreement, they may separate by one thinking or calling the other an optimist and the other thinking or calling his opponent a pessimist. Thereby they settle the matter temporarily, although of course they leave it undecided and agree only to differ. What they really settle is that two congenitally different temperaments necessarily view the subject from two different aspects and conclude accordingly. They do not stay to enquire which is the true view, the one being inclined by his temperament to look on the dark side of things and see the evils, hates, strifes, sufferings, failures and follies in the world, the other inclined by his temperament to look on their bright side and accordingly see the good, love, joys, and successes in it. Why, indeed, should they stop to enquire? Every mind in the world necessarily construes it in terms of itself, and therefore feels and thinks its individual world—the mind of the fool a different world from that of the sage, the mind of the sinner from that of the saint, the mind of the Andaman Islander from that of the Anglo-Saxon, the mind of the particular person from that of his neighbour. There must naturally be one common world in the necessarily common notion of a like-structured species, but there are as many particular worlds as there are persons in it.