DE FINE BONORUM. On the End of Goods.

35. Thus there are three ends the ultimate goals of life devoid of the honorable: one simple, of which Zeno is the author, placed entirely in decoration, that is, in the honorable.

15 Cicero, On Ends III 9, 31. It remains that the highest good is to live while applying the knowledge of those things which happen by nature, choosing things which are according to nature, and rejecting those which are against nature, that is, to live in a manner convenient and in agreement with nature.

16 Stobaeus, Eclogues II 76, 16 W. They say that the end is eudaimonia happiness/flourishing, for the sake of which all things are done, but which is done for the sake of nothing; and this consists in living according to virtue, in living consistently, and, since it is the same thing, in living according to nature. Zeno defined eudaimonia happiness in this way: happiness is a smooth flow of life. Cleanthes used this definition in his own writings, as did Chrysippus and all who followed them, saying that happiness is no different from a happy life, even though they say that happiness is set out as a target, and the end is to attain happiness, which is the same as being happy.
It is clear from these points that 'living according to nature' is equivalent to 'living well' and 'living successfully,' and again to 'the noble and good' and 'virtue and that which partakes of virtue'; and that every good is noble, and likewise every base thing is evil; for which reason the Stoic end is equal to a life lived in accordance with virtue.

17 Michael of Ephesus, On the Nicomachean Ethics (Commentaria in Aristotelem Graeca Vol. XX) ed. Heylb. p. 598, 20. That according to the assumptions of other philosophers, both the Epicureans and the later Stoics regarding happiness, one could grant happiness even to irrational animals, one might demonstrate through these points. If living according to nature, according to the Stoics, is living well, and living well, according to both them and Epicurus, is to be happy, then living according to nature is to be happy. But surely, living according to nature belongs to irrational animals from birth until their prime; therefore, irrational animals are happy.
p. 599, 6. Again, if happiness, according to the Stoics, is the final limit of natural appetite, which nature reaches to have the goal and the end, and having reached it, desires nothing more except to hold that very good proper to it and not lose it, and this also belongs to irrational animals, then irrational animals also partake in happiness.

18 Cicero, On Ends III 22. But from this, the error must first be removed, so that no one thinks that there are two ultimate goods. For just as if someone were proposed to aim a spear or an arrow at some target, just as we say the ultimate in goods is the goal, so they should do everything possible to hit it. In such a comparison, everything must be done so that one may hit it, and yet that one does everything to achieve the proposal is this, as it were, the final thing, which we call the highest good in life, while that hitting it is as if to be chosen, but not to be pursued.

19 Alexander of Aphrodisias, Quaestiones II 16 p. 61, 1 Bruns. If someone were to say that the end of the arts of conjecture arts that involve skill and probability, like medicine or navigation, as opposed to arts with absolute results is to do everything in their power toward hitting the target, how is it not the same for these arts as for those that are not arts of conjecture? They seem to differ from others most in this, that they do not hit the end in the same way. For those for whom the end is to attain the target, they would differ in this way; but for those for whom the aforementioned is their end, even if they do not hit the end in the same way, they would differ from them in not having the same end as them. For those non-conjectural arts, by the goal for which things are done following the things that happen according to the art, and the failure of the target following the error of the things being done not being done technically, have as their end the attainment of the target (for it is equal in those cases to have done everything in their power toward the attainment of the target, and to have attained it; for when they do these things, the things in their power come to pass). But in the case of the arts of conjecture, because the end for which things are done does not necessarily follow the things done according to the art, because they need many things to attain that, which are not solely in the art, and also because the things themselves done according to the art are not fixed, nor are they productive of the same results because they do not present themselves in the same way, because all things, or some things, are done differently within them, not as expected, the attainment of the target is not the end, but the fulfillment of the requirements of the art.