The first, supposes that opposition of will is possible, but insufficient;—for example: it is possible for me to place myself in opposition to a rushing torrent, but my opposition is insufficient, and the progress of the torrent relatively to me is necessary.
The second does not take will into consideration at all, and applies to subjects where opposition of will is not supposable; for example, logical necessity, a is b, and c is a, therefore c is b: mathematical necessity, 2 x 2 = 4. The centre of a circle is a point equally distant from every point in the circumference: metaphysical necessity, the existence of a first cause, of time, of space. Edwards comprehends this second kind of necessity under the general designation of metaphysical or philosophical. This second kind of necessity undoubtedly is absolute. It is impossible to conceive of these subjects differently from what they are. We cannot conceive of no space; no time; or that 2 x 2 = 5, and so of the rest.
Necessity under both points of view he distinguishes into particular and general.
Relative necessity, as particular, is a necessity relative to individual will; as general, relative to all will.
Metaphysical necessity, as particular, is a necessity irrespective of individual will; as general, irrespective of all will.
Relative necessity is relative to the will in the connexion between volition and its sequents. When a volition of individual will takes place, without the sequent aimed at, because a greater force is opposed to it, then the sequent of this greater force is necessary with a particular relative necessity. When the greater force is greater than all supposable will, then its sequents take place by a general relative necessity. It is plain however, that under all supposable will, the will of God cannot be included, as there can be no greater force than a divine volition.
Metaphysical necessity, when particular, excludes the opposition of individual will. Under this Edwards brings the connexion of motive and volition. The opposition of will, he contends, is excluded from this connexion, because will can act only by volition, and motive is the cause of volition. Volition is necessary by a particular metaphysical necessity, because the will of the individual cannot be opposed to it; but not with a general metaphysical necessity, because other wills may be opposed to it.
Metaphysical necessity, when general, excludes the opposition of all will—even of infinite will. That 2 x 2 = 4—that the centre of a circle is a point equally distant from every point in the circumference—the existence of time and space—are all true and real, independently of all will. Will hath not constituted them, nor can will destroy them. It would imply a contradiction to suppose them different from what they are. According to Edwards, too, the divine volitions are necessary with a general metaphysical necessity, because, as these volitions are caused by motives, and infinite will, as well as finite will, must act by volitions, the opposition of infinite will itself is excluded in the production of infinite volitions.
Now what is the simple idea of necessity contained in these two points of view, with their two-fold distinction? Necessity is that which is and which cannot possibly not be, or be otherwise than it is.
1. An event necessary by a relative particular necessity, is an event which is and cannot possibly not be or be otherwise by the opposition of an individual will.