Leibnitz denied an absolute reality to time, as he could not conceive of a reality which was out of relation to others, that is without force or energy. Time, accordingly, is with him merely ideal, phenomenal, with however a foundation in reality, namely, the order of succession of events. He transfers the real existence from time as a whole to the separate events which take place, change and activity being necessary and inseparable determinations of any real existence.
After Leibnitz attention is more and more directed towards our knowledge of time, how it is possible and what it involves, this phase reaching its theoretical completion in Kant. While Leibnitz held that time in us is only possible if there be a real succession, Kant insists on the other hand that the knowledge of succession presupposes that of time; — I could not regard two events as successive had I not already the notion of time as a whole, in which the events are arranged by me. Again, while I cannot think of phenomena as out of time, I can think of time as empty of events. Hence Kant decides that time is an a priori form in us, and is therefore no determination of reality as independent of us; while from the singleness of time, and the fact that every time is regarded as a part of this one time, he shows that it is a form of perception, not a concept. The latter argument is unimportant for our purpose; all knowledge is derived from perception, and concepts are abstracted from it. It is not even necessary that there should be two or more objects given, in order that a concept may be formed. Time itself, when thought of, that is, when its existence is abstracted from, is also a concept. Time as a whole, in fact, is never perceived, but is only an inference from the given parts. The gist of Kant’s argument lies in the fact of there being only one time, which is homogeneous throughout its parts, while the parts are not thought of as examples of a general type, but as parts of one whole. A second argument, which seeks to show that the time-form is given independently of experience, inasmuch as there exist absolutely necessary propositions concerning it, and these cannot be given through experience, need not delay us. Should time have a reality independent of our consciousness, Kant holds, then it would be impossible for us to form such a necessarily valid proposition as “Time has only one dimension.” This may be granted, but, as a matter of fact, no proposition that we can form is absolutely and necessarily valid, but is valid only under the condition that our knowledge is complete, and of this we can never be certain. Thus in a spherical space two straight lines may cut one another in two distinct points: in this way we have enlarged our notions of space, geometry no longer giving absolutely necessary
