to objects and events. It is especially against this position that Leibniz argues, holding that space and time are simply orders or relations of objects and events, that space exists only where objects are existing, and that it is the order of their co-existence, or of their possible co-existence; while time exists only as events are occurring, and is the relation of their succession. Clarke, on the other hand, speaks of the universe of objects as bounded by and moving about in an empty space, and says that time existed before God created the finite world, so that the world came into a time already there to receive its on-goings, just as it fell into a space already there to receive its co-existences.
To get at the ideas of Leibniz, therefore, we cannot do better than follow the course of this discussion. He begins by saying that both space and time are purely relative, one being the order of co-existences, the other of successions. Space characterizes in terms of possibility an order of things existing at the same time, so far as they exist in mutual relations (ensemble), without regard to their special modes of existence. As to the alternate doctrine that space is a substance, or something absolute, it contradicts the principle of sufficient reason. Were space something absolutely uniform, without things placed in it, there would be no difference between one part and another, and it would be a matter of utter indifference to God why he gave bodies certain positions in space rather than others; similarly it would be a matter of indifference why he created the world when he did, if time were something independent of events. In other words, the supposed absoluteness of space and time would render the action of God wholly without reason, capricious, and at haphazard. Similarly, it contradicts the principle of “indiscernibles,” by which Leibniz means the principle of specification, or distinction. According to him, to suppose two things exactly alike, is simply to imagine the same thing twice. Absolute uniformity, wholly undifferentiated, is a fiction impossible to realize in thought. “Space considered without objects has nothing in it to determine it; it is accordingly nothing actual. The parts of space must be determined and distinguished by the objects which are in them.” Finally, were space and time absolutely real things in themselves, they would be independent of God, and even limitations upon him. “They would be more substantial than substances. God would not be able to change or destroy them. They would be immutable and eternal in every part. Thus there would be an infinity of eternal things (these parts) independent of God.” They would limit God because he would be obliged to exist in them. Only by existing through this independent time would he be eternal; only by extending through this independent space would he be omnipresent. Space and time thus become gods themselves.
When Clarke declares that by the absoluteness of space and time he does not mean that they are themselves substances, but only properties, attributes of substance, Leibniz advances the same arguments in different form. If space were the property of the things that are in space, it would belong now to one substance, now to another, and when empty of all material substance, even to an immaterial substance, perhaps to God. “Truly a strange attribute which is handed about from one thing to another. Substances thus leave their accidents as if they were old clothes, and other substances put them on.” Since these finite spaces are in infinite space, and the latter is an attribute of God, it must be that an attribute of God is composed of parts, some of them empty, some full, some round, some square. So, too, whatever is in time would help make one of the attributes of God. “Truly a strange God,” says Leibniz, “this Deity of parts” (ce Dieu à parties). Clarke’s reply to this was that space and time are attributes of God and of God alone, not of things in space and time,—that, indeed, strictly speaking, there are no parts in space or in time; they are absolutely one. This was virtually to give up the whole matter. It was to deny the existence of finite spaces and times, and to resolve them into an indefinite attribute of God. Such a view, as Leibniz points out, not only is contrary to experience, but affords no aid in determining the actual concrete forms and situations of bodies, and durations and successions of events. The absolute space and time, having no parts, are wholly out of relations to these concrete existences. The latter require, therefore, a space and a time that are relations or orders. Clarke’s hypothesis is, as Leibniz says, wholly without use or function, and requires a theory like that of Leibniz to account for the actually determinate forms of experience. In his last reply Clarke shifts his ground again, and says that space and time are effects of God’s existence; “they are the necessary results of his existence.” “His existence is the cause of space and time.” The death of Leibniz prevented any further reply. It is not hard to imagine, however, that in a general way his reply would have been to ask how space and time are at once attributes essential and necessary to God, as constituting his immensity and eternity, and effects dependent upon his existence. To take this latter position, indeed, seems to abandon the position that they are absolute, and to admit that, like the rest of God’s creation, they are relative and finite.
So much for Leibniz’s polemic. Its meaning is that space and time have significance only with reference to things and events, that they are the intellectual, the ideal side of these objects and occurrences, being the relations which give them order and unity. A space which is not the space of objects, which is not space in and through objects, is an inanity; it is not spirit, it is not matter; it is not a relation of either. It is nothingness magnified to infinity, and then erected into existence. And all for nothing; for it does not enable us to account for a single concrete fact of experience. For this we must have recourse to relations and orders of existence. Space is therefore to be defined as the order which makes it possible for objects to have situation; time as that which makes it possible for events to have dating,—not as if they were actually prior to them, and although nothings in themselves, yet capable of giving concrete determination to things, but as actually the relations themselves, and as ideally necessary for the coherent experience of co-existent objects and of connected events. As Leibniz puts it epigrammatically: “Space is the order of possible constants; time the order of inconstant possibilities.”
We have finished the exposition of the views of Leibniz about matter and material facts. One question, however, remains to be discussed,—a question which Leibniz’s contemporary critics would not allow him to pass over in silence, even had he been so disposed. What is the reality of matter, of motion, of space, and of time? Since they are, as Leibniz says, only phenomena, not absolute realities, what distinguishes them from dreams, from illusions? What distinguishes sensible phenomena from capricious fantasies, and gives them reality?
Leibniz begins his answer by pointing out that the mere fact that bodies are phenomena does not make them unreal. To say that anything is phenomenal is to say that it is sensible; but “the senses make no declaration regarding metaphysical matters” such as truth and reality. The senses, in a word, only inform us that the experiences are there for the senses, that they are sensible. What is the ultimate nature of the sensible or the phenomenal, what is their reality, is a question wholly outside the province of sense. The questions of ultimate nature, of reality, are questions of metaphysics, and hence are to be decided by the reason, not by the senses. And Leibniz goes on to say that the truthfulness of the senses, since it concerns only the sensible, consists in the reciprocal agreement of sensible facts, and in that we are not deceived in reasoning from one to another. An isolated sense-experience could not be said to be either true or false, real or illusory. It would be true that it was experienced, and that is all that could be said about it. But since our experiences are not thus separated, but have a certain order, there arises what we may call sensible reality and illusion. When the order between two facts remains the same “in different times and places and in the experience of different men,” we call these facts real. If, however, our experience cannot be repeated by ourselves or by other men when the same conditions (that is, connections) are present, it is unreal, or false. It is thus “the relation of phenomena which guarantees truth of fact regarding sensible objects.” Constancy, regularity, justify us in ascribing reality; chaotic change and lack of orderly connection are a sign of unreality. Even our dreams have a reality; for they have their connections and place in experience. If we understood their connections we should even be able to explain their apparent lack of connection with the rest of experience. Leibniz thinks that both the Academicians and Sceptics and their opponents erred in attempting to find greater reality in sensible things than that of regular phenomena. Since our observations and judgments upon
