1911 Encyclopædia Britannica/Necessity
NECESSITY (Lat. necessitas), a term used technically in philosophy for the quality of inevitable happening; for example, hot air necessarily tends to rise. Thus it corresponds in the sphere of action to certainty in the sphere of knowledge. That the sun will rise to-morrow is a necessary event; and men anticipate the rising with certainty. In ordinary language the conception of necessity is rendered meaningless by being referred to the present or even to the past. A current definition of necessity is "the state which cannot be otherwise than it is." Such a definition tells us nothing. How can any state be otherwise than it is? Necessity can have meaning only in reference to the future: it means absence of spontaneous power in that which acts necessarily. For the origin of the conception we must look to our inward personal experience of constraint. When we are acting under physical or mathematical or logical or moral necessity we are so far precluded from spontaneous action—in common phrase, we can do no otherwise—though the causes of constraint may be of very different kinds. In ethics the term necessitarianism is applied to that view of human action which regards all action as dictated by external causes (cf. Determinism). The sense in which, if at all, the human mind can cognize necessity, i.e. causal connexion between events or states, has been the subject of vigorous discussion among philosophers. By sceptics and empiricists it is held that a law is merely a crystallized summary of observed phenomena. Thus J. S. Mill denies that a general proposition is more than an enumeration of particulars, and hence that syllogistic reasoning cannot amplify knowledge (see Syllogism). It is clear that the senses cannot apprehend causal connexion, and this impossibility gives rise to a prior conception according to which the conception of necessity is purely intellectual (see Metaphysics).