§5.5ἀναγκαῖον λέγεται οὗ ἄνευ οὐκ ἐνδέχεται ζῆν ὡς συναιτίου (οἷον τὸ ἀναπνεῖν καὶ ἡ τροφὴ τῷ ζῴῳ ἀναγκαῖον, ἀδύνατον γὰρ ἄνευ τούτων εἶναι), καὶ ὧν ἄνευ τὸ ἀγαθὸν μὴ ἐνδέχεται ἢ εἶναι ἢ γενέσθαι, ἢ τὸ κακὸν ἀποβαλεῖν ἢ στερηθῆναι (οἷον τὸ πιεῖν τὸ φάρμακον ἀναγκαῖον ἵνα μὴ κάμνῃ, καὶ τὸ πλεῦσαι εἰς Αἴγιναν ἵνα ἀπολάβῃ τὰ χρήματα).
'Necessary' is spoken of, in one way, as that without which, as a joint cause, it is not possible to live (for instance, breathing and food are necessary for an animal, for it is impossible to exist without these); and as those things without which good cannot either be or come to be, or without which one cannot discard or be rid of evil (for instance, drinking medicine is necessary in order not to be sick, and sailing to Aegina in order to recover one's money).
ἔτι τὸ βίαιον καὶ ἡ βία· τοῦτο δʼ ἐστὶ τὸ παρὰ τὴν ὁρμὴν καὶ τὴν προαίρεσιν ἐμποδίζον καὶ κωλυτικόν, τὸ γὰρ βίαιον ἀναγκαῖον λέγεται, διὸ καὶ λυπηρόν (ὥσπερ καὶ Εὔηνός φησι
"πᾶν γὰρ ἀναγκαῖον πρᾶγμʼ ἀνιαρὸν ἔφυ"
), καὶ ἡ βία ἀνάγκη τις (ὥσπερ καὶ Σοφοκλῆς λέγει
"ἀλλʼ ἡ βία με ταῦτʼ ἀναγκάζει ποιεῖν"
), καὶ δοκεῖ ἡ ἀνάγκη ἀμετάπειστόν τι εἶναι, ὀρθῶς· ἐναντίον γὰρ τῇ κατὰ τὴν προαίρεσιν κινήσει καὶ κατὰ τὸν λογισμόν.
Further, the forced and force; and this is that which impedes and prevents, contrary to impulse and choice. For the forced is said to be necessary, wherefore it is also painful (as Evenus also says, "For every necessary thing is by nature painful"), and force is a certain necessity (as Sophocles also says, "But force necessitates me to do these things"). And necessity is thought to be something that cannot be persuaded, and rightly so; for it is contrary to the motion which is in accordance with choice and reasoning.
ἔτι τὸ μὴ ἐνδεχόμενον ἄλλως ἔχειν ἀναγκαῖόν φαμεν οὕτως ἔχειν· καὶ κατὰ τοῦτο τὸ ἀναγκαῖον καὶ τἆλλα λέγεταί πως ἅπαντα ἀναγκαῖα·
Further, we say that that which cannot be otherwise is necessarily so; and it is in accordance with this sense of the necessary that all other things are also, in some way, called necessary.
τό τε γὰρ βίαιον ἀναγκαῖον λέγεται ἢ ποιεῖν ἢ πάσχειν τότε, ὅταν μὴ ἐνδέχηται κατὰ τὴν ὁρμὴν διὰ τὸ βιαζόμενον, ὡς ταύτην ἀνάγκην οὖσαν διʼ ἣν μὴ ἐνδέχεται ἄλλως, καὶ ἐπὶ τῶν συναιτίων τοῦ ζῆν καὶ τοῦ ἀγαθοῦ ὡσαύτως· ὅταν γὰρ μὴ ἐνδέχηται ἔνθα μὲν τὸ ἀγαθὸν ἔνθα δὲ τὸ ζῆν καὶ τὸ εἶναι ἄνευ τινῶν, ταῦτα ἀναγκαῖα καὶ ἡ αἰτία ἀνάγκη τίς ἐστιν αὕτη.
For the forced is said to do or suffer what is necessary then, when it is not possible to act in accordance with impulse because of that which forces—implying that this force is a necessity because of which it is not possible to be otherwise. And the same holds for the joint causes of living and of the good; for when either the good, or living and being, is not possible without certain things, these things are necessary and this cause is a certain necessity.
ἔτι ἡ ἀπόδειξις τῶν ἀναγκαίων, ὅτι οὐκ ἐνδέχεται ἄλλως ἔχειν, εἰ ἀποδέδεικται ἁπλῶς· τούτου δʼ αἴτια τὰ πρῶτα, εἰ ἀδύνατον ἄλλως ἔχειν ἐξ ὧν ὁ συλλογισμός.
Further, demonstration belongs to the necessary, because it is not possible for a thing to be otherwise if it has been demonstrated without qualification; and the causes of this are the primary premises, if the premises from which the syllogism proceeds cannot be otherwise.
τῶν μὲν δὴ ἕτερον αἴτιον τοῦ ἀναγκαῖα εἶναι, τῶν δὲ οὐδέν, ἀλλὰ διὰ ταῦτα ἕτερά ἐστιν ἐξ ἀνάγκης.
Therefore, of some necessary things, something else is the cause of their being necessary, but of others nothing is, but rather other things are of necessity because of them.
ὥστε τὸ πρῶτον καὶ κυρίως ἀναγκαῖον τὸ ἁπλοῦν ἐστίν· τοῦτο γὰρ οὐκ ἐνδέχεται πλεοναχῶς ἔχειν, ὥστʼ οὐδὲ ἄλλως καὶ ἄλλως· ἤδη γὰρ πλεοναχῶς ἂν ἔχοι.
Consequently, the primary and strictly necessary is the simple; for this cannot be in many states, and therefore not in one state and then in another, for then it would already be in many states.
εἰ ἄρα ἔστιν ἄττα ἀΐδια καὶ ἀκίνητα, οὐδὲν ἐκείνοις ἐστὶ βίαιον οὐδὲ παρὰ φύσιν.
If, then, there are certain eternal and immovable things, nothing is forced or contrary to nature for them.