And although pleasure is desirable for its own sake, still they admit that some of the efficient causes of it are often troublesome, and as such opposite to pleasure; so that they think that an assemblage of all the pleasures which produce happiness, is the most difficult thing conceivable. But they admit that every wise man does not live pleasantly, and that every bad man does not live unpleasantly, but that it is only a general rule admitting of some exceptions. And they think it sufficient if a person enjoys a happy time in consequence of one pleasure which befalls him. They say that prudence is a good, but is not desirable for its own sake, but for the sake of those things which result from it. That a friend is desirable for the sake of the use which we can make of him; for that the parts of the body also are loved while they are united to the body; and that some of the virtues may exist even in the foolish. They consider that bodily exercise contributes to the comprehension of virtue; and that the wise man will feel neither envy, nor love, nor superstition; for that these things originate in a fallacious opinion. They admit, at the same time, that he is liable to grief and fear, for that these are natural emotions. They said also that wealth is an efficient cause of pleasure, but that it is not desirable for its own sake. That the sensations are things which can be comprehended; but they limited this assertion to the sensations themselves, and did not extend it to the causes which produce them. They left out all investigation of the subjects of natural philosophy because of the evident impossibility of comprehending them; but they applied themselves to the study of logic, because of its utility. Meleager, in the second book of his Treatise on Opinions and Clitomachus in the first book of his Essay on Sects says, that they thought natural philosophy and dialectics useless for that the man who had learnt to understand the question of good and evil could speak with propriety, and was free from superstition, and escaped the fear of death, without either. They also taught that there was nothing naturally and intrinsically just, or honourable, or disgraceful; but that things were considered so because of law and fashion. The good man will do nothing out of the way, because of the punishments which are imposed on, and the discredit which is attached to, such actions: and that the good man is a wise man. They admit, too, that there is such a thing as improvement in philosophy, and in other good studies. And they say that one man feels grief more than another; and that the sensations are not always to be trusted as faithful guides.