Necessary, Necessity. The schoolmen distinguished between two kinds of necessity, necessitas consequentiœ and necessitas consequentis. The former is a relation between thoughts, judgments, and propositions, the relation of premisses to a conclusion, the latter a relation between things and events, the relation of cause and effect. In the former case necessity does not involve truth. Suppose the syllogism to be good as such, it may have false premisses, and from those premisses there may come a conclusion as false as themselves, but it will necessarily follow from them. I might say, «All Englishmen love liberty; Philip II. was an Englishman, therefore Philip II. loved liberty,» in which case my minor premiss and my conclusion would both be staringly false, but the conclusion would be a necessary result of the premisses.
In strictly abstract matter necessity always prevails, and its nature is such that we feel not only what is propounded to be true, but that there would be contradiction and absurdity in supposing it otherwise. Necessary truth as such is universal. There may be no triangles in a distant fixed star, but if there are we are sure that their three angles must be together equal to two right angles. Of course only what is necessary admits of demonstration.
Moral necessity is that which is commonly meant when we speak of the doctrine of necessity. According to that doctrine, motives act as forces on the conduct, the relation between the two being strictly that of cause and effect. When two motives are present, as when two forces, the strongest will prevail. The whole universe, the moral and spiritual no less than the physical, is thus one adamantine chain of causes and effects. (See Liberty and Will.)
The contrary of the former, which may be called logical necessity, is contingency; of the latter, moral necessity, is liberty. Most people, of whom I confess I am one, view the latter as involved in the very idea of will. Indeed the necessitarian cannot be said to recognise will at all, since he makes the dependence of conduct on motive immediate, and he can therefore only mean by will susceptibility of motive.
