HE most important of the affections which concern the whole body remains to be considered-that is, the cause of pleasure and pain in the perceptions of which I have been speaking, and in all other things which are perceived by sense through the parts of the body, and have both pains and pleasures attendant on them. Let us imagine the causes of every affection, whether of sense or not, to be of the following nature, remembering that we have already distinguished between the nature which is easy and which is hard to move; for this is the direction in which we must hunt the prey which we mean to take. A body which is of a nature to be easily moved, on receiving an impression however slight, spreads abroad the motion in a circle, the parts communicating with each other, until at last, reaching the principle of mind, they announce the quality of the agent. But a body of the opposite kind, being immobile, and not extending to the surrounding region, merely receives the impression, and does not stir any of the neighbouring parts; and since the parts do not distribute the original impression to other parts, it has no effect of motion on the whole animal, and therefore produces no effect on the patient. This is true of the bones and hair and other more earthy parts of the human body; whereas what was said above relates mainly to sight and hearing, because they have in them the greatest amount of fire and air. Now we must conceive of pleasure and pain in this way. An impression produced in us contrary to nature and violent, if sudden, is painful; and, again, the sudden return to nature is pleasant; but a gentle and gradual return is imperceptible and vice versa.

ἡδονὴ καὶ λύπη

[64a] Μέγιστον δὲ καὶ λοιπὸν τῶν κοινῶν περὶ ὅλον τὸ σῶμα παθημάτων τὸ τῶν ἡδέων καὶ τῶν ἀλγεινῶν αἴτιον ἐν οἷς διεληλύθαμεν͵ καὶ ὅσα διὰ τῶν τοῦ σώματος μορίων αἰσθήσεις κεκτημένα καὶ λύπας ἐν αὑτοῖς ἡδονάς θ΄ ἅμα ἑπομένας ἔχει. ὧδ΄ οὖν κατὰ παντὸς αἰσθητοῦ καὶ ἀναισθήτου παθήματος τὰς αἰτίας λαμβάνωμεν͵ [64b] ἀναμιμνῃσκόμενοι τὸ τῆς εὐκινήτου τε καὶ δυσκινήτου φύσεως ὅτι διειλόμεθα ἐν τοῖς πρόσθεν· ταύτῃ γὰρ δὴ μεταδιωκτέον πάντα ὅσα ἐπινοοῦμεν ἑλεῖν. τὸ μὲν γὰρ κατὰ φύσιν εὐκίνητον͵ ὅταν καὶ βραχὺ πάθος εἰς αὐτὸ ἐμπίπτῃ͵ διαδίδωσιν κύκλῳ μόρια ἕτερα ἑτέροις ταὐτὸν ἀπεργαζόμενα͵ μέχριπερ ἂν ἐπὶ τὸ φρόνιμον ἐλθόντα ἐξαγγείλῃ τοῦ ποιήσαντος τὴν δύναμιν· τὸ δ΄ ἐναντίον ἑδραῖον ὂν κατ΄ οὐδένα τε κύκλον ἰὸν πάσχει μόνον͵ [64c] ἄλλο δὲ οὐ κινεῖ τῶν πλησίον͵ ὥστε οὐ διαδιδόντων μορίων μορίοις ἄλλων ἄλλοις τὸ πρῶτον πάθος ἐν αὐτοῖς ἀκίνητον εἰς τὸ πᾶν ζῷον γενόμενον ἀναίσθητον παρέσχεν τὸ παθόν. ταῦτα δὲ περί τε ὀστᾶ καὶ τὰς τρίχας ἐστὶν καὶ ὅσ΄ ἄλλα γήϊνα τὸ πλεῖστον ἔχομεν ἐν ἡμῖν μόρια· τὰ δὲ ἔμπροσθεν περὶ τὰ τῆς ὄψεως καὶ ἀκοῆς μάλιστα͵ διὰ τὸ πυρὸς ἀέρος τε ἐν αὐτοῖς δύναμιν ἐνεῖναι μεγίστην. τὸ δὴ τῆς ἡδονῆς καὶ λύπης ὧδε δεῖ διανοεῖσθαι· [64d] τὸ μὲν παρὰ φύσιν καὶ βίαιον γιγνόμενον ἁθρόον παρ΄ ἡμῖν πάθος ἀλγεινόν͵ τὸ δ΄ εἰς φύσιν ἀπιὸν πάλιν ἁθρόον ἡδύ͵ τὸ δὲ ἡρέμα καὶ κατὰ σμικρὸν ἀναίσθητον͵ τὸ δ΄ ἐναντίον τούτοις ἐναντίως.