Necessity

Necessity [Lat. necessitas]: Ger. Nothwendigkeit; Fr. nécessité; Ital. necessità. (1) The state or condition that cannot be otherwise than it is; that must be just as it is.

(2) The principle in virtue of which the condition of the universe as a whole, or any particular part of it, is rendered, both as to its existence and quality, inevitable. Opposed to both freedom and chance, but especially, in its strictly philosophical use, to chance […] or contingency. That which has the property of necessity is said to be necessary.

…when knowledge is indeterminate among alternatives, either there is one state of things which alone accords with them all, when this is in the Mode of Necessity, or there is more than one state of things that no knowledge excludes, when each of these is in the Mode of Possibility.

Necessity […] is that mode of being which is not subject to the principle of excluded middle, since it may neither be that A is necessarily B, nor that A is necessarily not B. [—] How can the principle of excluded middle fail to apply? By the function of determination being given over to the person addressed.

…the Necessary […] is that which tends to govern both Thought and real Fact, even should it never become absolute in either sway.