I know there are some who pretend that the idea of duration is applicable in a proper sense to objects which are perfectly unchangeable; and this I take to be the common opinion of philosophers as well as of the vulgar. But to be convinced of its falsehood, we need but reflect on the foregoing conclusion, that the idea of duration is always derived from a succession of changeable objects, and can never be conveyed to the mind by any thing stedfast and unchangeable. For it inevitably follows from thence, that since the idea of duration cannot be derived from such an object, it can never in any propriety or exactness be applied to it, nor can any thing unchangeable be ever said to have duration. Ideas always represent the objects or impressions, from which they are derived, and can never, without a fiction, represent or be applied to any other. By what fiction we apply the idea of time, even to what is unchangeable, and suppose, as is common that duration is a measure of rest as well as of motion, we shall consider afterwards.[4] There is another very decisive argument, which establishes the present doctrine concerning our ideas of space and time, and is founded only on that simple principle, _that our ideas of them are compounded of parts, which are indivisible_. This argument may be worth the examining. Every idea that is distinguishable being also separable, let us take one of those simple indivisible ideas, of which the compound one of _extension_ is formed, and separating it from all others, and considering it apart, let us form a judgment of its nature and qualities. 'Tis plain it is not the idea of extension: for the idea of extension consists of parts; and this idea, according to the supposition, is perfectly simple and indivisible. Is it therefore nothing? That is absolutely impossible. For as the compound idea of extension, which is real, is composed of such ideas, were these so many nonentities there would be a real existence composed of nonentities, which is absurd. Here, therefore, I must ask, _What is our idea of a simple and indivisible point_? No wonder if my answer appear somewhat new, since the question itself has scarce ever yet been thought of. We are wont to dispute concerning the nature of mathematical points, but seldom concerning the nature of their ideas.