Still, there remains the question, How can this be possible? and this is no easy one to answer. The contemporary opponents of the Stoics already took exception to the way in which the first demands of nature were by them excluded from the aims of a life [703] according to nature; and we, too, cannot suppress a feeling of perplexity at being told that all duties aim at attaining what is primarily according to nature, but that what is according to nature must not be looked upon as the aim of our actions; [704] since not that which is simply according to nature, but the rational choice and combination of what is according to nature constitutes the good. [705] Even if the Stoics pretend to dispose of this difficulty, they cannot, at least, fail to see that whatever contributes to bodily well-being must have a certain positive value, and must be desirable in all cases in which no higher good suffers in consequence; and, conversely, that whatever is opposed to bodily well-being, when higher duties are not involved, must have a negative value (ἀπαξία), and, consequently, deserve to be avoided. [706] Such objects and actions they would not, however, allow to be included in the class of goods which are absolutely valuable. [707] It was therefore a blending of Peripatetic with Stoic teaching when Herillus, the fellow-student of Cleanthes, enumerated bodily and outward goods as secondary and subsidiary aims besides virtue. [708] [(2) Classes of things indifferent.] Nor were the Stoics minded to follow the contemporary philosopher, Aristo of Chios (who in this point, too, endeavoured to place their School on the platform of the Cynic philosophy), in denying any difference in value between things morally indifferent [709] and in making the highest aim in life consist in indifference to all external things. [710] Virtue with them bears, in comparison with the Cynic virtue, a more positive character, that of an energetic will; they, therefore, required some definite relation to the outward objects and conditions of this activity which should regulate the choosing or rejecting—or, in other words, the practical decision. Accordingly, they divided things indifferent into three classes. To the first class belong all those things which, from a moral or absolute point of view, are neither good nor evil, but yet which have a certain value; no matter whether this value belongs to them properly, because they are in harmony with human nature, or whether it belongs to them improperly, because they are means for advancing moral and natural life, or whether it belongs to them on both grounds. The second class includes everything which, either by itself or in its relation to higher aims, is opposed to nature and harmful. The third, things which, even in this conditional sense, have neither positive nor negative value. The first class bears the name of things preferential (προηγμένον), or things desirable; the second is the class of things to be eschewed