Again, this very thing is the virtue of the happy man and the perfect happiness of life when everything is done according to a harmony with the genius of each individual with reference to the will of the universal governor and manager of all things. Diogenes, accordingly, says expressly that the chief good is to act according to sound reason in our selection of things according to our nature. And Archedemus defines it to be living in the discharge of all becoming duties. Chrysippus again understands that the nature, in a manner corresponding to which we ought to live, is both the common nature, and also human nature in particular; but Cleanthes will not admit of any other nature than the common one alone, as that to which people ought to live in a manner corresponding; and repudiates all mention of a particular nature. And he asserts that virtue is a disposition of the mind always consistent and always harmonious; that one ought to seek it out for its own sake, without being influenced by fear or hope by any external influence. Moreover, that it is in it that happiness consists, as producing in the soul the harmony of a life always consistent with itself; and that if a rational animal goes the wrong way, it is because it allows itself to be misled by the deceitful appearances of exterior things, or perhaps by the instigation of those who surround it; for nature herself never gives us any but good inclinations. LIV. Now virtue is, to speak generally, a perfection in everything, as in the case of a statue; whether it is invisible as good health, or speculative as prudence. For Hecaton says, in the first book of his treatise on Virtues, that the scientific and speculative virtues are those which have a constitution arising from speculation and study, as, for instance, prudence and justice; and that those which are not speculative are those which are generally viewed in their extension as a practical result or effect of the former; such for instance, as health and strength. Accordingly, temperance is one of the speculative virtues, and it happens that good health usually follows it, and is marshalled as it were beside it; in the same way as strength follows the proper structure of an arch.—And the unspeculative virtues derive their name from the fact of their not proceeding from any acquiescence reflected by intelligence; but they are derived from others, are only accessories, and are found even in worthless people, as in the case of good health, or courage. And Posidonius, in the first book of his treaties on Ethics, says that the great proof of the reality of virtue is that Socrates, and Diogenes, and Antisthenes, made great improvement; and the great proof of the reality of vice may be found in the fact of its being opposed to virtue.