in reaching the conclusion that the problem of knowledge 

 could only be solved by a study of the facts of consciousness, 

 that is, ideas. Locke's contribution to this investigation is 

 specifically the analysis of complex ideas, and the reaching of 

 those elements or materials out of which all ideas were made, 

 and on the basis of which all our knowledge must be reached. 

 Locke claimed that all the facts of consciousness are analys- 

 able into ideas of sensation and ideas of reflection. 1 Ideas of 

 sensation include all the properties commonly called by the 

 name sensations, which are mediated to us through the sense 

 organs from the operation of external objects upon them. 

 Ideas of reflection are the ideas which we have of the operations 

 of our own minds, such as perceiving, remembering, thinking, 

 willing, etc. In their arising, all of these ideas of sensation 

 and reflection are simple ; that is, they cannot be analysed into 

 anything more elementary. As Locke says: "Each in itself 

 is uncompounded.' ' 2 Further, these ideas cannot be changed 

 by the mind in any way. It cannot alter them, nor make unto 

 itself any new idea not received in these ways. 3 Out of these 

 materials, as the elements and foundations of all ideas, the 

 mind, by compounding, comparing, and abstracting, is able to 

 make all the complex ideas which we have. Some of these 

 ideas, both simple and complex, have natural or rational rela- 

 tions to one another. And from the perception of these rela- 

 tions, all our knowledge is built up. Others of them, "ideas that 

 in themselves are not at all of kin' ' 4 have no natural or rational 

 relations, and the fact that they are related at all is due solely 

 to chance or custom. This relation, which Locke calls a kind 

 of ' 'madness' ', and which he thinks to be the foundation of the 

 bitter differences of opinion and prejudice found in politics and 

 religion among other things, he calls Association of Ideas, to 

 distinguish it from the natural or rational relation. In this 

 association of ideas, Locke discovered a fact which is, in reality, 

 true of all combinations of simple ideas. It was to be the work 

 of Berkeley, and Hume in particular, to enunciate more 

 clearly than Locke had done, the significance of this fact. The 

 formula which expresses it, is stated by Hume in his Treatise, 

 viz., "Whatever objects are different are distinguishable, and 

 whatever objects are distinguishable are separable by the 

 thought and imagination." 5 The significance of ^ this state- 

 ment is just that no combination or relation of simple ideas 



'John Locke, "Essay on the Human Understanding", 1690. Bk. II, Ch. 1. 



2 O.C. II, 2, 1. 



3 O.C. II, 1, 25. 



*O.C. 11,33, 5. 



5 David Hume, "Treatise on Human Nature", Pt. I, 7. 



