Duration and succession, eternity and time, are not identical. Duration is the continuance in existence of finite creatures, a continuance which is measured by the equable motion of planetary orbs, and imperfectly by phenomenal changes in our mental states. Succession is simply an order of phenomena, the recurrence, at regular or irregular intervals, of like changes, or the series of different states in the same existence. Time is a certain correlation of successive existences. Eternity is an attribute of the absolute Being—the timelessness of God. He is not subject to the law of change, and therefore not to the law of time, therefore his absolute being can not be measured by successive epochs.
Let us now endeavor to dismiss from our thought all this perplexing necromancy of words, and humbly pray, with Themistocles, for "some sweet voluptuous art of forgetting." Let us fix our mental gaze upon the objects of thought which are denoted by the terms time and space, and ask what are they? Are they existences or attributes, are they ideal or real, are they entities or relations? Have we any clear and definite notions of which these are the unequivocal signs? The solution of these questions is the essential condition of a true philosophy of time and space.
First of all, is it not self-evident that, if time and space are for us the objects of thought, they must be conceived under the categories of Being or Quality or Relation? If they can not be thought as real existences, or as attributes of existing things, or as relations among existing things, they can not be thought at all—they are non-entities, and we can not think about nothing. "Thought can only be realized by thinking something ... this something must be thought as existing ... and we can only think a thing as existing, by thinking it as existing in this or that determinate manner of existence; and whenever we cease to think of something as existing—something existing in a determinate manner of existence—we cease to think at all."[100]
McCosh asserts that time and space are "neither substances, modes, nor relations."[101] What, then, are they? He answers, "They seem to be entitled to be put in a class by themselves, and resemble substances, modes, relations only in that they are existences, entities, realities."[102] But if they are entitled to be put in a class by themselves, what is the name of that class, and by what characteristic marks shall we distinguish it? If they are realities, they must have being, or inhere in something that has being, or be relations of something in being. If they are existences, they must be the objects of sense perception, or rational intuition, or immediate judgment, otherwise they can not be cognized at all, for "the mind can not create objects of its own cognition."
We ask again, What are space and time? McCosh and Dr. Porter both answer: 1. They are not substances. This no one will dispute. They are not material substances having sensible qualities which can be the objects of sense perception. Space and time are not perceived by the senses.[103] Neither are they spiritual substances. We do not know them as having power and performing acts. 2. They both reply, They are not attributes or qualities of matter or spirit. This, also, no one will dispute, if the word "time" is not used as a synonym for "eternity," and the word "space" is not used as a synonym for "immensity," because "eternity" and "immensity" are attributes of the absolute Spirit. 3. They both assert, They are not relations. This is disputed by many: by Leibnitz, by Hamilton, by Saisset, by Calderwood, and by others. Leibnitz says, "Space is the order of things co-existing. Time is the order of things successive."[104] Hamilton says, "Space, like time, is only the intuition or the conception of a certain correlation of existence."[105] Calderwood defines time "as a certain correlation of existence," and "space as the recognized relation of extended objects."[106] And Saisset regards time and space as standing in the same category with mathematical relations.[107] These are, to say the least, distinguished names in philosophy. The opinions of men who have for years pondered these profound problems are at any rate entitled to proper consideration, and if in opposition to their views it is affirmed that time and space as understanding-concepts are not relations, some reasons should be assigned. All the proof offered by Dr. McCosh is that "we know no two or more things which by their relation could yield space and time" (p. 211). We answer, promptly, duration and change do yield the relation of time. "The consciousness of succession in our mental states is in reality our consciousness of time."[108] The co-existence of two or more extended objects must yield the relation of space, for "empty space is nothing more than the relative distance of extended objects from each other, measured on a standard similar to that which applies to the bodies themselves. In this way it is equally accurate to say that there is a certain specified distance between the bodies, and that there is nothing between them, because space is nothing but their relation to each other."[109] Annihilate all finite existences, and what remains? Nothing but the immensity of God. Let one atom of matter be created, and we have extension. Let a second atom be created, and there is now a relation of distance, position, direction—that is, there is space.
The only remark made by Dr. Porter which has a direct bearing on this important discussion is that "Space and time are neither relations nor correlations, but correlates to beings and events" ("The Human Intellect," p. 568). It may seem an act of presumption in one who has spent much less time on these studies than Dr. Porter to offer a criticism on this final deliverance. But when he tells us that space and time are neither relations nor correlations, after having through four pages "On the relations of space and time concepts to motion" labored to sustain the doctrine of Trendelenberg that "the categories of space and time are derived from the universal and all-pervading motion which is common to both" (p. 526), we confess we are amazed. Let it be granted that the spatial and temporal relations can be, in their last analysis, resolved into motion, still the question remains, How can we conceive of motion except as the result of force?—that is, of power actually exerted somewhere. In the last analysis, therefore, the relations of space, time, and motion are resolved into "the relation of causality." The conclusion seems inevitable that time and space are correlations of finite existences. Annihilate all finite existences and finite duration, and there is neither space nor time—that is, there is "pure nothing." Or, more properly, there is the Omnipotence, the Immensity, the Eternity of God, whose causation may give existence to finite beings with all their necessary as well as contingent relations. "Whoever maintains a beginning of the world must also adopt a beginning of time, for only worldly being, which according to its notion has not its ground in itself, but is an originated being, can at all have time for the form of its existence."[110]
And now, in summing up, let us see if we can clearly disengage three classes of distinct notions:
1. The notion of concrete and finite EXTENSION as the essential quality of matter; and the notion of finite DURATION as a quality of changeful dependent existence.
2. The notion of SPACE as the relation of co-existing material things—that is, the relation of position, distance, direction, hereness, thereness; and the notion of time as the relation of successive existence—that is, the relation of priority and posteriority, of past, present, and future.
3. The notion of IMMENSITY and ETERNITY—that is, an absolute continuity and illimitability of being, the absence of all limit, all quantity, all beginning and end, the attributes of the unconditioned Being. Let us endeavor sharply to define these notions, which unhappily are too often confounded.