8. The abstrusest Ideas we can have are all from two Sources.
If we trace the progress of our minds, and with attention observe how it repeats, adds together, and unites its simple ideas received from sensation or reflection, it will lead us further than at first perhaps we should have imagined. And, I believe, we shall find, if we warily observe the originals of our notions, that EVEN THE MOST ABSTRUSE IDEAS, how remote soever they may seem from sense, or from any operations of our own minds, are yet only such as the understanding frames to itself, by repeating and joining together ideas that it had either from objects of sense, or from its own operations about them: so that those even large and abstract ideas are derived from sensation or reflection, being no other than what the mind, by the ordinary use of its own faculties, employed about ideas received from objects of sense, or from the operations it observes in itself about them, may, and does, attain unto.
This I shall endeavour to show in the ideas we have of space, time, and infinity, and some few others that seem the most remote, from those originals.
CHAPTER XIII.
COMPLEX IDEAS OF SIMPLE MODES:—AND FIRST, OF THE SIMPLE MODES OF IDEA OF SPACE.
1. Simple modes of simple ideas.
Though in the foregoing part I have often mentioned simple ideas, which are truly the materials of all our knowledge; yet having treated of them there, rather in the way that they come into the mind, than as distinguished from others more compounded, it will not be perhaps amiss to take a view of some of them again under this consideration, and examine those different modifications of the SAME idea; which the mind either finds in things existing, or is able to make within itself without the help of any extrinsical object, or any foreign suggestion.
Those modifications of any ONE simple idea (which, as has been said, I call SIMPLE MODES) are as perfectly different and distinct ideas in the mind as those of the greatest distance or contrariety. For the idea of two is as distinct from that of one, as blueness from heat, or either of them from any number: and yet it is made up only of that simple idea of an unit repeated; and repetitions of this kind joined together make those distinct simple modes, of a dozen, a gross, a million. Simple Modes of Idea of Space.
2. Idea of Space.
I shall begin with the simple idea of SPACE. I have showed above, chap. 4, that we get the idea of space, both by our sight and touch; which, I think, is so evident, that it would be as needless to go to prove that men perceive, by their sight, a distance between bodies of different colours, or between the parts of the same body, as that they see colours themselves: nor is it less obvious, that they can do so in the dark by feeling and touch.