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.

3.  Space and Extension.

This space, considered barely in length between any two beings, without considering anything else between them, is called distance:  if considered in length, breadth, and thickness, I think it may be called capacity.  When considered between the extremities of matter, which fills the capacity of space with something solid, tangible, and moveable, it is properly called extension.  And so extension is an idea belonging to body only; but space may, as is evident, be considered without it.  At lest I think it most intelligible, and the best way to avoid confusion, if we use the word extension for an affection of matter or the distance of the extremities of particular solid bodies; and space in the more general signification, for distance, with or without solid matter possessing it.

4.  Immensity.

Each different distance is a different modification of space; and each idea of any different distance, or space, is a simple mode of this idea.  Men having, by accustoming themselves to stated lengths of space, which they use for measuring other distances—­as a foot, a yard or a fathom, a league, or diameter of the earth—­made those ideas familiar to their thoughts, can, in their minds, repeat them as often as they will, without mixing or joining to them the idea of body, or anything else; and frame to themselves the ideas of long, square, or cubic feet, yards or fathoms, here amongst the bodies of the universe, or else beyond the utmost bounds of all bodies; and, by adding these still one to another, enlarge their ideas of space as much as they please.  The power of repeating or doubling any idea we have of any distance, and adding it to the former as often as we will, without being ever able to come to any stop or stint, let us enlarge it as much as we will, is that which gives us the idea of immensity.

5.  Figure.