For, First, by observing what passes in our minds, how our ideas there in train constantly some vanish and others begin to appear, we come by the idea of SUCCESSION. Secondly, by observing a distance in the parts of this succession, we get the idea of DURATION. Thirdly, by sensation observing certain appearances, at certain regular and seeming equidistant periods, we get the ideas of certain LENGTHS or MEASURES OF DURATION, as minutes, hours, days, years, &c. Fourthly, by being able to repeat those measures of time, or ideas of stated length of duration, in our minds, as often as we will, we can come to imagine DURATION,—WHERE NOTHING DOES REALLY ENDURE OR EXIST; and thus we imagine to-morrow, next year, or seven years hence. Fifthly, by being able to repeat ideas of any length of time, as of a minute, a year, or an age, as often as we will in our own thoughts, and adding them one to another, without ever coming to the end of such addition, any nearer than we can to the end of number, to which we can always add; we come by the idea of ETERNITY, as the future eternal duration of our souls, as well as the eternity of that infinite Being which must necessarily have always existed. Sixthly, by considering any part of infinite duration, as set out by periodical measures, we come by the idea of what we call TIME in general. CHAPTER XV. IDEAS OF DURATION AND EXPANSION, CONSIDERED TOGETHER. 1. Both capable of greater and less. Though we have in the precedent chapters dwelt pretty long on the considerations of space and duration, yet, they being ideas of general concernment, that have something very abstruse and peculiar in their nature, the comparing them one with another may perhaps be of use for their illustration; and we may have the more clear and distinct conception of them by taking a view of them together. Distance or space, in its simple abstract conception, to avoid confusion, I call EXPANSION, to distinguish it from extension, which by some is used to express this distance only as it is in the solid parts of matter, and so includes, or at least intimates, the idea of body: whereas the idea of pure distance includes no such thing. I prefer also the word expansion to space, because space is often applied to distance of fleeting successive parts, which never exist together, as well as to those which are permanent. In both these (viz. expansion and duration) the mind has this common idea of continued lengths, capable of greater or less quantities. For a man has as clear an idea of the difference of the length of an hour and a day, as of an inch and a foot. 2. Expansion not bounded by Matter.