mind between those which are offered to the sight by the different perceptible distances of a body in motion, or between sounds or smells following one another; there also the sense of a constant continued succession is lost, and we perceive it not but with certain gaps of rest between.
The mind cannot fix long on one invariable idea.§ 13. If it be so that the ideas of our minds, whilst we have any there, do constantly change and shift in a continual succession, it would be impossible, may any one say, for a man to think long of any one thing. By which, if it be meant that a man may have one self-same single idea a long time alone in his mind, without any variation at all, I think, in matter of fact, it is not possible; for which (not knowing how the ideas of our minds are framed, of what materials they are made, whence they have their light, and how they come to make their appearances) I can give no other reason but experience: and I would have any one try whether he can keep one unvaried single idea in his mind, without any other, for any considerable time together.
§ 14. For trial, let him take any figure, any degree of light or whiteness, or what other he pleases; and he will, I suppose, find it difficult to keep all other ideas out of his mind: but that some, either of another kind, or various considerations of that idea (each of which considerations is a new idea) will constantly succeed one another in his thoughts, let him be as wary as he can.
§ 15. All that is in a man's power in this case, I think, is only to mind and observe what the ideas are that take their turns in his understanding; or else to direct the sort, and call in such as he hath a desire or use of: but hinder the constant succession of fresh ones, I think, he cannot, though he may commonly choose whether he will heedfully observe and consider them.
Ideas, however made,§ 16. Whether these several ideas in a man's mind be made by certain motions,
