11. Again, _great_ and _small_, _swift_ and _slow_, are allowed to exist nowhere without the mind(547); being entirely relative, and changing as the frame or position of the organs of sense varies. The extension therefore which exists without the mind is neither great nor small, the motion neither swift nor slow; that is, they are nothing at all. But, say you, they are extension in general, and motion in general. Thus we see how much the tenet of extended moveable substances existing without the mind depends on that strange doctrine of _abstract ideas_. And here I cannot but remark how nearly the vague and indeterminate description of Matter, or corporeal substance, which the modern philosophers are run into by their own principles, resembles that antiquated and so much ridiculed notion of _materia prima_, to be met with in Aristotle and his followers. Without extension solidity cannot be conceived: since therefore it has been shewn that extension exists not in an unthinking substance, the same must also be true of solidity(548).
12. That _number_ is entirely the creature of the mind(549), even though the other qualities be allowed to exist without, will be evident to whoever considers that the same thing bears a different denomination of number as the mind views it with different respects. Thus, the same extension is one, or three, or thirty-six, according as the mind considers it with reference to a yard, a foot, or an inch. Number is so visibly relative, and dependent on men's understanding, that it is strange to think how any one should give it an absolute existence without the mind. We say one book, one page, one line, &c.; all these are equally units, though some contain several of the others. And in each instance, it is plain, the unit relates to some particular combination of ideas _arbitrarily_ put together by the mind(550).
13. Unity I know some(551) will have to be a simple or uncompounded idea, accompanying all other ideas into the mind. That I have any such idea answering the word _unity_ I do not find; and if I had, methinks I could not miss finding it; on the contrary, it should be the most familiar to my understanding, since it is said to accompany all other ideas, and to be perceived by all the ways of sensation and reflexion. To say no more, it is an _abstract idea_.