We cannot investigate pleasure (Sokrates continues) apart from pain: both must be studied together. Both pleasure and pain reside in the third out of the four above-mentioned Genera:[30] that is, in the compound Genus formed out of that union (of the Infinite with the Determinans or Finient) which includes all animated bodies. Health and Harmony reside in these animated bodies: and pleasure as well as pain proceed from modifications of such fundamental harmony. When the fundamental harmony is disturbed or dissolved, pain is the consequence: when the disturbance is rectified and the harmony restored, pleasure ensues.[31] Thus hunger, thirst, extreme heat and cold, are painful, because they break up the fundamental harmony of animal nature: while eating, drinking, cooling under extreme heat, or warming under extreme cold, are pleasurable, because they restore the disturbed harmony.
[30] Plato, Philêbus, p. 31 C. ἐν τῷ κοινῷ μοι γένει ἅμα φαίνεσθον λύπη τε καὶ ἡδονὴ γίγνεσθαι κατὰ φύσιν … κοινὸν τοίνυν ὑπακούωμεν ὃ δὴ τῶν τεττάρων τρίτον ἐλέγομεν. Compare p. 32 A-B: τὸ ἐκ τοῦ ἀπείρου καὶ πέρατος κατὰ φύσιν ἔμψυχον γεγονὸς εἶδος.
Plato had before said that ἡδονὴ belonged to the Infinite (compare p. 41 D), or to the first of the four above-mentioned genera, not to the third.
[31] Plato, Philêbus, p. 31 D.
This is the primary conception, or original class, of pleasures and pains, embracing body and mind in one and the same fact. Pleasure cannot be had without antecedent pain: it is in fact a mere reaction against pain, or a restoration from pain.
Derivative pleasures of memory and expectation belonging to mind alone. Here you may find pleasure without pain.
But there is another class of pleasures, secondary and derivative from these, and belonging to the mind alone without the body. The expectation of future pleasures is itself pleasurable,[32] the expectation of future pains is itself painful. In this secondary class we find pleasure without pain, and pain without pleasure: so that we shall be better able to study pleasure by itself, and to decide whether the whole class, in all its varieties, be good, welcome and desirable, — or whether pleasure and pain be not, like heat and cold, desirable or undesirable according to circumstances — i.e. not good in their own nature, but sometimes good and sometimes not.[33]
[32] Plato, Philêbus, p. 32 C. ἡδονῆς καὶ λύπης ἕτερον εἶδος, τὸ χωρὶς τοῦ σώματος αὐτῆς τῆς ψυχῆς διὰ προσδοκίας γιγνόμενον.
[33] Plato, Philêbus, p. 32 D.