13. Locke, recapitulating his theory of ideas, illustrates it in the following manner :

"These alone," (sensation and reflection) "as far as I can discover, are the windows by which light is let into this dark room; for methinks the understanding is not much unlike a closet wholly shut from light, with only some little opening left to let in external visible resemblances, or ideas of things without: would the pictures coming into such a dark room but stay there, and lie so orderly as to be found upon occasion, it would very much resemble the understanding of a man in reference to the objects of sight, and the ideas of them." B. 2. Ch. XI. ý 17.

This illustration is evidently borrowed from Plato. He illustrates the manner in which we perceive external objects of sense, by supposing a dark cave in which men are so bound, that they can only view one part of it. Behind this, at a distance, is a light, some rays of which pass over a wall to that part of the cave which is before the eyes of those who are confined in it. Various objects pass between them and the light, the shadows of which they behold, but not the objects themselves. Locke, however, seems to confine the illustration to perceptions of sight.

LECTURE X.

Division of Complex Ideas. Idea of space and its modes. Extension not body.

1. COMBINATIONS of simple ideas frequently enter the mind from external objects, and are looked on as complex ideas, without having been connected together by any immediate act of the mind. In this way Locke thinks it probable that brutes receive complex ideas. (Lect. IX. §6.) By far the greater number of our complex are, however, wholly made by and receive their unity from an act of the mind, and even those collections of simple ideas which are received from external objects are subsequently rendered more exact types of the originals from whence they were taken, by mental operations.

2. The classes of complex ideas, according to Locke, and which are sometimes called his Categories, are

1. Modes.

2. Substances.

3. Relations.

1o. Modes in general are "such complex ideas, which however compounded, contain not in them the supposition of subsisting by themselves, but are considered as dependences on, or affections of substances." Modes are twofold, simple and mixed. Simple modes are compounded of repetitions of the same simple idea. The component

M

simple ideas in a mixed mode are different, Locke uses the word "modes" in these cases, "out of its ordinary signification." But where it is necessary to communicate a new notion, it must be done either by inventing a new term or using an old one in a new sense. He thinks the latter preferable.

2o. Substances are "those combinations of simple ideas, as are taken to represent distinct particular things subsisting by themselves, in which the supposed or confused idea of substance, such as it is, is always first and chief." Substances are divided into single, as they are considered to exist separately, as a man or a sheep, and collective where several are put together, as an army, a flock.

3o. Relations are those complex ideas which arise from the comparison of two ideas in any respect.

3. In the examination of our ideas, Locke commences with the simple modes of space and time. He assumes as self-evident that we obtain the idea of space both by sight and touch. Space may be considered in three respects. 1° When it is considered "barely as length between any two beings," it is called distance. 2°. When considered as having length, breadth, and thickness, it is called capacity. 3o. Considered in the abstract, it is called extension.

4. The idea of immensity is obtained by repeating without limit the idea of a finite space. Figure, another modification of space, is "the relation which the parts of the termination of extension or circumscribed space have amongst themselves." The infinite variety of this class of ideas appears from the vast number of figures which really exist, as well as from the unlimited power of the mind in varying the idea of figure.

Place is the relation of distance between any thing and any two or more points which are considered in keeping the same distance one with another, and so considered at rest." The necessity of fixed points to determine

place is manifest from our inability to determine the place of the universe.

5. Locke takes occasion in treating of space to impugn the Cartesian doctrine, that space is inseparable from body. He considers that the impossibility of solidity existing independently of extension, is not a proof of extension being inseparable from body, as many ideas require others as necessary to their existence, and yet the ideas may be perfectly different. Thus scarlet colour cannot exist without extension, and yet these are distinct ideas. He states also, that if spirit be admitted to be different from body because it has not extension, it must also be admitted, that space is different from body because it has not solidity. In fine he thinks extension or space different from body, for three reasons.

1o. Because extension includes neither the idea of solidity nor its consequence, resistance; and body includes both.

2o. Because the parts of space are inseparable really or mentally, and the parts of body are separable both really and mentally.

[To divide actually or really is by removing the parts from one another to produce two surfaces where before there was but one. To divide mentally is to imagine this done.]

3o. The parts of space are immoveable, and those of body moveable.

6. Extension has been defined to be that which has partes extra partes. This Locke translates, "that which has extended parts exterior to extended parts." This as a definition is defective, because the term to be defined is introduced into it; the absurdity of which he illustrates by comparing it to defining a fibre to be that which is made up of several fibres. He considers that extension being a simple idea does not allow of definition. (See Lect. III. § 5.)

The following dilemma has been brought to prove that space cannot exist without body:

Space is either something or nothing.

If nothing be between two bodies they touch.

If something be between them, it must be either body or spirit.

...There is no space, &c.

This is a petitio principii, for it assumes that all beings are included under body and spirit, whereas the very point in question is, whether there is not a third being, viz.

space.

7. Locke thinks that those who deny the existence of pure space must suppose body infinite; for if body were finite it would be impossible not to suppose space beyond its limits. Let a man placed at the bounds of body stretch forth his hand, and he must stretch it into pure space. He also thinks that they must deny to the Creator the power of annihilation, for if they grant that, they must at least grant the possibility of a vacuum. He conceives that the motions of the bodies of the universe prove the existence of pure space, for if space was completely filled with matter, no motion could take place; for no solid body could be conceived to be so divided that the parts would move freely amongst each other.