92. I agree that the idea of time is not derived from mere experience; for experience could not furnish an element so solid and so fixed, on which we may with perfect security rest all the observations of science. Still less can it be maintained, that the idea of time is derived from purely sensible experience, or that it is in itself a sensation. 93. The idea of time is not a sensation; for it is relative, and sensation is an affection of our being, without any reference to or comparison with any thing. When we experience sensations, if we had only the sensitive faculty, we should be limited to pure sensation, without any consideration of before or after, or any relation of any kind. Sensation, being limited to certain objects, cannot, like the idea of time, extend to all objects. By time, we measure not only the external world, but also the internal; not only the affections of the body, but also the most concealed and abstract actions of our mind. Time is, in itself, succession, and, in our mind, it is the perception of this succession; it cannot, therefore, present any object to the mind; even when time refers to objects, and is, as it were, the link between them, it is not itself either these objects themselves, nor the intuition of them. The idea of the time which measures the succession of a sound or of a sight, clearly is not either the sound or the sight, but the perception of their succession, of their connection. If it were the sight alone, or the sound alone, either the sight or the sound would alone be sufficient in order to perceive time, which is absurd; for there is no time without succession, and consequently there can be no time which measures two sensations without these sensations. The idea of time is independent of either of the two; it is superior to them; it is a sort of universal form, independent of this or that matter; so that, if after the sound, instead of the sight, another sound should be perceived by us, the measure of the succession would be the same, and this measure is nothing more than the idea of time. Sensations being mere contingent facts, cannot be the foundation of necessary and universal truths, they cannot serve as the basis of a science. But the idea of time is one of the principal ideas in all the physical sciences, and, like extension, is subjected to a very rigorous calculation; therefore, it is not a sensation, and it is not derived from sensation.