Like the Cynics and Stoics, he rejected the world and all its conventions and prizes, its desires and passions and futility. But where the Stoic and Cynic proclaimed that in spite of all the pain and suffering of a wicked world, man can by the force of his own will be virtuous, Epicurus brought the more surprising good news that man can after all be happy. But to make this good news credible he had to construct a system of thought. He had to answer the temple authorities and their adherents among the vulgar, who threatened his followers with the torments of Hades for their impiety. He had to answer the Stoics and Cynics, preaching that all is worthless except Aretê; and the Sceptics, who dwelt on the fallibility of the senses, and the logical impossibility of knowledge. He met the last of these by the traditional Ionian doctrine of sense-impressions, ingeniously developed. We can, he argued, know the outer world, because our sense impressions are literally 'impressions' or stamps made by external objects upon our organs. To see, for instance, is to be struck by an infinitely tenuous stream of images, flowing from the object and directly impinging upon the retina. Such streams are flowing from all objects in every direction--an idea which seemed incredible until the modern discoveries about light, sound, and radiation. Thus there is direct contact with reality, and consequently knowledge. Besides direct vision, however, we have 'anticipations', or προλήψεις, sometimes called 'common conceptions', e. g. the general conception which we have of a horse when we are not seeing one. These are merely the result of repeated acts of vision. A curious result of this doctrine was that all our 'anticipations' or 'common ideas' are true; mistakes occur through some interpretation of our own which we add to the simple sensation.