49. THE STEP TO IDEALISM.--The admirable clearness with which Locke writes makes it the easier for his reader to detect the untenability of his position. He uses simple language, and he never takes refuge in vague and ambiguous phrases. When he tells us that the mind is wholly shut up to its ideas, and then later assumes that it is not shut up to its ideas, but can perceive external things, we see plainly that there must be a blunder somewhere. George Berkeley (1684-1753), Bishop of Cloyne, followed out more rigorously the consequences to be deduced from the assumption that all our direct knowledge is of ideas; and in a youthful work of the highest genius entitled "The Principles of Human Knowledge," he maintained that there is no material world at all. When we examine with care the objects of sense, the "things" which present themselves to us, he argues, we find that they resolve themselves into sensations, or "ideas of sense." What can we mean by the word "apple," if we do not mean the group of experiences in which alone an apple is presented to us? The word is nothing else than a name for this group as a group. Take away the color, the hardness, the odor, the taste; what have we left? And color, hardness, odor, taste, and anything else that may be referred to any object as a quality, can exist, he claims, only in a perceiving mind; for such things are nothing else than sensations, and how can there be an unperceived sensation? The things which we perceive, then, he calls complexes of ideas. Have we any reason to believe that these ideas, which exist in the mind, are to be accepted as representatives of things of a different kind, which are not mental at all? Not a shadow of a reason, says Berkeley; there is simply no basis for inference at all, and we cannot even make clear what it is that we are setting out to infer under the name of matter. We need not, therefore, grieve over the loss of the material world, for we have suffered no loss; one cannot lose what one has never had. Thus, the objects of human knowledge, the only things of which it means anything to speak, are: (1) Ideas of Sense; (2) Ideas of Memory and Imagination; (3) The Passions and Operations of the Mind; and (4) The Self that perceives all These. From Locke's position to that of Berkeley was a bold step, and it was much criticised, as well it might be. It was felt then, as it has been felt by many down to our own time, that, when we discard an external world distinct from our ideas, and admit only the world revealed in our ideas, we really do lose.