"These simple ideas, the materials of all our knowledge, are suggested and furnished to the mind only by those two ways above mentioned, namely, Sensation and Reflection. When the Understanding is once stored with these simple ideas, it has the power to repeat, compare, and unite them, even to an almost infinite variety, and so can make at pleasure new complex ideas. But it is not in the power of the most exalted Wit or enlarged Understanding, by any quickness or variety of thoughts, to invent or frame one new simple idea in the mind, not taken in by the ways before mentioned. Nor can any force of the Understanding destroy those that are there: the dominion of man, in this little world of his own understanding, being much-what the same as it is in the great world of visible things, wherein his power, however managed by art and skill, reaches no farther than to compound and divide the materials that are made to his hand, but can do nothing towards the making the least particle of new matter or destroying one atom of what is already in being. The same inability will every one find in himself who shall go about to fashion in his Understanding any simple idea not received in by his senses from external objects or by reflection from the operations of his own mind about them." (Bk. II., ch. ii., § 2.) In the reception of these simple ideas, Locke regards the mind as merely passive. It can no more refuse to have them, alter or blot them out, than a mirror can refuse to receive, alter, or obliterate the images reflected on it. The Understanding, before the entrance of simple ideas, is like a dark room, and external and internal sensation are the windows by which light is let in. But when the light has once penetrated into this dark recess, the Understanding has an almost unlimited power of modifying and transforming it. It can create complex ideas, and that in an infinite variety, out of its simple ideas, and this it does chiefly by combining, comparing, and separating them. "This shows man's power, and its way of operation, to be much what the same in the material and intellectual world. For the materials in both being such as he has no power over, either to make or destroy, all that man can do is either to unite them together, or to set them by one another, or wholly separate them." (Bk. II., ch. xii., § 1.) The complex ideas are classified under three heads, modes, which may be either simple or mixed, substances, and relations. Here, however, my analysis must stop, and I must content myself with giving a few examples of the manner in which Locke attempts to resolve "complex ideas" into "simple" ones.