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.
(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 Evenus Footnote 1Of Poros; sophist and poet, contemporary with Socrates. says: For every necessary thing is by nature grievous.
Footnote 2Evenus Fr. 8 (Hiller).
And compulsion is a kind of necessity, as Sophocles says: Compulsion makes me do this of necessity.
Footnote 3Soph. El. 256 (the quotation is slightly inaccurate).
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.
It is from this sense of necessary
that all others are somehow derived; for the term compulsory
is used of something which it is necessary for one to do or suffer only when it is impossible to act according to impulse, because of the compulsion: which shows that necessity is that because of which a thing cannot be otherwise; and the same is true of the concomitant conditions of living and of the good. For when in the one case good, and in the other life or existence, is impossible without certain conditions, these conditions are necessary, and the cause is a kind of necessity.
(e) Again, demonstration is a necessary
thing, because a thing cannot be otherwise if the demonstration has been absolute. And this is the result of the first premisses, when it is impossible for the assumptions upon which the syllogism depends to be otherwise.
Thus of necessary things, some have an external cause of their necessity, and others have not, but it is through them that other things are of necessity what they are.
Hence the necessary
in the primary and proper sense is the simple , for it cannot be in more than one condition. Hence it cannot be in one state and in another; for if so it would ipso facto be in more than one condition. Therefore if there are certain things which are eternal and immutable, there is nothing in them which is compulsory or which violates their nature.