Necessity and Contingency

Thus far in what we have been saying, with small exception, the works of intelligence have been set forth; and now we must place by the side of them in our discourse the things which come into being through necessity—for the creation is mixed, being made up of necessity and mind. Mind, the ruling power, persuaded necessity to bring the greater part of created things to perfection, and thus and after this manner in the beginning, when the influence of reason got the better of necessity, the universe was created. But if a person will truly tell of the way in which the work was accomplished, he must include the other influence of the variable cause as well. Wherefore, we must return again and find another suitable beginning, as about the former matters, so also about these.

We call ‘necessary’ (1, a) that without which, as a condition, a thing cannot live; e.g. breathing and food are necessary for an animal; for it is incapable of existing without these; (b) the conditions without which good cannot be or come to be, or without which we cannot get rid or be freed of evil; e.g. drinking the medicine is necessary in order that we may be cured of disease, and a man’s sailing to Aegina is necessary in order that he may get his money.-(2) The compulsory and compulsion, i.e. that which impedes and tends to hinder, contrary to impulse and purpose. For the compulsory is called necessary (whence the necessary is painful, as Evenus says: ‘For every necessary thing is ever irksome’), and compulsion is a form of necessity, as Sophocles says: ‘But force necessitates me to this act’. And necessity is held to be something that cannot be persuaded-and rightly, for it is contrary to the movement which accords with purpose and with reasoning.-(3) We say that that which cannot be otherwise is necessarily as it is. And from this sense of ‘necessary’ all the others are somehow derived; for a thing is said to do or suffer what is necessary in the sense of compulsory, only when it cannot act according to its impulse because of the compelling forces-which implies that necessity is that because of which a thing cannot be otherwise; and similarly as regards the conditions of life and of good; for when in the one case good, in the other life and being, are not possible without certain conditions, these are necessary, and this kind of cause is a sort of necessity.

The word "necessity" is employed in many ways. For that which must be is necessary. Now that a thing must be may belong to it by an intrinsic principle---either material, as when we say that everything composed of contraries is of necessity corruptible---or formal, as when we say that it is necessary for the three angles of a triangle to be equal to two right angles. And this is "natural" and "absolute necessity." In another way, that a thing must be, belongs to it by reason of something extrinsic, which is either the end or the agent. On the part of the end, as when without it the end is not to be attained or so well attained: for instance, food is said to be necessary for life, and a horse is necessary for a journey. This is called "necessity of end," and sometimes also "utility." On the part of the agent, a thing must be, when someone is forced by some agent, so that he is not able to do the contrary. This is called "necessity of coercion."