Book 5
1
Necessary means: (a) That without which, as a concomitant condition, life is impossible; e.g. respiration and food are necessary for an animal, because it cannot exist without them. (b) The conditions without which good cannot be or come to be, or without which one cannot get rid or keep free of evil—e.g., drinking medicine is necessary to escape from ill-health, and sailing to Aegina is necessary to recover one’s money.
2
(c) The compulsory and compulsion; i.e. that which hinders and prevents, in opposition to impulse and purpose. For the compulsory is called necessary, and hence the necessary is disagreeable; as indeed EvenusOf Poros; sophist and poet, contemporary with Socrates. says: For every necessary thing is by nature grievous. Evenus Fr. 8 (Hiller).
3
And compulsion is a kind of necessity, as Sophocles says: Compulsion makes me do this of necessity. Soph. El. 256 (the quotation is slightly inaccurate).
3
And necessity is held, rightly, to be something inexorable; for it is opposed to motion which is in accordance with purpose and calculation. (d) Again, what cannot be otherwise we say is necessarily so.
