The enquiry into the destiny and end of man turns, with the Stoics, as it did with all moral philosophers since the time of Socrates, about the fundamental conception of the good, and the ingredients necessary to make up the highest good or happiness. [521] Happiness, they consider, can only be sought in rational activity or virtue. Speaking more explicitly, [522] the primary impulse of every being is towards self-preservation and self-gratification. [523] It follows that every being pursues those things which are most suited to its nature, [524] and that such things only have for it a value (ἀξία). Hence the highest good—the end-in-chief, [525] or happiness—can only be found in what is conformable to nature. [526]—Nothing can be conformable to nature for any individual thing, unless it be in harmony with the law of the universe, [527] or with the universal reason of the world; nor, in the case of a conscious and reasonable being, unless it proceeds from a recognition of this general law—in short, from rational intelligence. [528] In every enquiry into what is conformable to nature, all turns upon agreement with the essential constitution of the being, and this essential constitution consists, in the case of a man, simply in reason. [529] One and the same thing, therefore, is always meant, whether, with Zeno, life according to nature is spoken of as being in harmony with oneself, or whether, following Cleanthes, it is simply said to be the agreement of life with nature, and whether, in the latter case, φύσις is taken to mean the world at large, or is limited to human nature in particular. [530] In every case the meaning is, that the life of the individual approximates to or falls short of the goal of happiness, exactly in proportion as it approaches to or departs from the universal law of the world and the particular rational nature of man. In a word, a rational life, an agreement with the general course of the world, constitutes virtue. The principle of the Stoic morality might therefore be briefly expressed in the sentence: Only virtue is good, and happiness consists exclusively in virtue. [531] If, however, following Socrates, the good is defined as being what is useful, [532] then the sentence would run thus: Only Virtue is useful; advantage cannot be distinguished from duty, whilst to a bad man nothing is useful, [533] since, in the case of a rational being, good and evil does not depend on what happens to him, but simply on his own conduct. [534] A view of life is here presented to us in which happiness coincides with virtue, the good and the useful with duty and reason. There is neither any good independently of virtue, nor is there in virtue and for virtue any evil. [(2) The good and evil.]