We must remember that the future is neither wholly ours nor wholly not ours, so that neither must we count upon it as quite certain to come nor despair of it as quite certain not to come. And of the necessary desires some are necessary if we are to be happy, some if the body is to be rid of uneasiness, some if we are even to live. He who has a clear and certain understanding of these things will direct every preference and aversion toward securing health of body and tranquillity of mind, seeing that this is the sum and end of a happy life. When we are pained, then, and then only, do we feel the need of pleasure. For this reason we call pleasure the alpha and omega of a happy life.
Pleasure is our first and kindred good.
It is the starting-point of every choice and of every aversion, and to it we come back, inasmuch as we make feeling the rule by which to judge of every good thing. And since pleasure is our first and native good, for that reason we do not choose every pleasure whatever, but often pass over many pleasures when a greater annoyance ensues from them. And often we consider pains superior to pleasures when submission to the pains for a long time brings us as a consequence a greater pleasure. It is, however, by measuring one against another, and by looking at the conveniences and inconveniences, that all these matters must be judged. Sometimes we treat the good as an evil, and the evil, on the contrary, as a good.