In Epicurean philosophy, pleasure is any experience in life which is not felt to be pain. All experiences in life are felt to be either pleasure or pain. There is no neutral experience, or any experience other than that which can be classified as pleasure or pain. Therefore in Epicurean philosophy it is also true that pain is any experience in life which is not felt to be pleasure.
Citations:
Diogenes Laertius: "The internal sensations they say are two, pleasure and pain, which occur to every living creature, and the one is akin to nature and the other alien: by means of these two choice and avoidance are determined."
Epicurus: PD03. "The limit of quantity in pleasures is the removal of all that is painful. Wherever pleasure is present, as long as it is there, there is neither pain of body, nor of mind, nor of both at once."
Torquatus: "Now what facts does [Nature] grasp or with what facts is her decision to seek or avoid any particular thing concerned, unless the facts of pleasure and pain?"
Torquatus: "For the pleasure which we pursue is not that alone which excites the natural constitution itself by a kind of sweetness, and of which the sensual enjoyment is attended by a kind of agreeableness, but we look upon the greatest pleasure as that which is enjoyed when all pain is removed. Now inasmuch as whenever we are released from pain, we rejoice in the mere emancipation and freedom from all annoyance, and everything whereat we rejoice is equivalent to pleasure, just as everything whereat we are troubled is equivalent to pain, therefore the complete release from pain is rightly termed pleasure. For just as the mere removal of annoyance brings with it the realization of pleasure, whenever hunger and thirst have been banished by food and drink, so pain is removed. For just as the mere removal of annoyance brings with it the realization of pleasure, whenever hunger and thirst have been banished by food and drink, so in every case the banishment of pain ensures its replacement by pleasure."
Torquatus: [[38] "Therefore Epicurus refused to allow that there is any middle term between pain and pleasure; what was thought by some to be a middle term, the absence of all pain, was not only itself pleasure, but the highest pleasure possible. Surely any one who is conscious of his own condition must needs be either in a state of pleasure or in a state of pain."
Torquatus: "My father used to say that even a statue would not talk in that way, if it had power of speech. The inference is shrewd enough as against the Cyrenaics, but does not touch Epicurus. For if the only pleasure were that which, as it were, tickles the senses, if I may say so, and attended by sweetness overflows them and insinuates itself into them, neither the hand nor any other member would be able to rest satisfied with the absence of pain apart from a joyous activity of pleasure. But if it is the highest pleasure, as Epicurus believes, to be in no pain, then the first admission, that the hand in its then existing condition felt no lack, was properly made to you, Chrysippus, but the second improperly, I mean that it would have felt a lack had pleasure been the supreme good. It would certainly feel no lack, and on this ground, that anything which is cut off from the state of pain is in the state of pleasure."
Others: (to be added)
Note: This is a draft of an entry for Pleasure*. The reason for the asterisk is that otherwise the Lexicon will link every appearance of the word pleasure in every context, and while that might have desirable aspects it would be overwhelming to have so many links. Adding the asterisk allows an easy citation to this reference, just as we may add a similar entry for Gods*.