phenomena of the mind as having an existence independent of material objects. The trees, and stones, and other objects which we know, and as we know them, exist away outside of us, and the mind which knows exists somewhere within the body; and these two things, the external material bodies and the mind, are totally different in nature and independent in existence. And the problem of psychology is to determine how it is that the mind knows the objects of the material world, and what amount of confidence is to be placed in this knowledge. This is what we might call the stand-point of practical common sense. The practical man, with his sensive organism completely matured and educated, sees objects in the world around him apparently existing independently of his mind; and when he becomes a philosopher his great question naturally is how these objects, which are extended, figured, and distant, can be perceived by his mind, which is an unextended spiritual substance. Thus there is assumed the existence of two worlds, differing in nature and independent in existence, and then the question is asked, how does the one come to know the other, how does mind know matter? For the sake of distinctness, and for want of a better name, we may call this the stand-point of practical dualism. (2) Those who adopt the second point of view assume nothing regarding the existence or nature of an external world, but analyse all their knowledge into its original elements, as found in consciousness; and, beginning with the simplest facts given in CHAP. III. SECT. I. CHAP. III. SECT. I. Origin of representationism. consciousness, seek to discover the manner in which the sphere of our knowledge and belief is gradually filled up. As a preliminary to the adoption of this method, it is necessary that nearly all our naturally acquired beliefs regarding the existence and nature of objects of sense should, for the time, be given up. The object of the psychologist is to determine the origin and process of the acquisition of knowledge, and, therefore, it is not legitimate to assume anything regarding the existence and nature of the objects of knowledge until it is seen how they have become objects. From this, which we may call the philosophical point of view, the student works his way from within outwards, beginning with those facts of consciousness, which, as far as he can discover, are elementary, endeavouring to discover what they reveal of the non-ego, and how they are combined or modified, and in no case assuming anything which they do not give. One or other of these points of departure has been adopted, and adhered to with greater or less consistency, by nearly all modern philosophers. We shall not at present express any opinion as to their respective merits, but proceed to examine the theories of perception which may be classed under them respectively. § 41. We have said that the problem which the psychologists who adopt the first method require to solve is, to determine how two independently existing and heterogeneous substances can have communication the one with the other. Given, that there exists a mind, spiritual and unextended; that outside, in space, there exist material bodies possessing various qualities; how does the former come to know or believe in the latter? The answers to this question have been various, and at present we shall not attempt any exact classification of them, as, indeed, perhaps no classification could be made without in some way doing violence to the theories concerned. Generally speaking it has been held that mind can have no immediate knowledge of matter, and that knowledge can only be effected by the intermediation of some image or idea, which either represents or suggests the external object. The fundamental principle which appears to underlie the most of the theories of this kind is that the mind cannot directly know anything but its own ideas, and consequently these theories have been classed together under such names as idealism, representative idealism, cosmothetic idealism, &c. But it is to be borne in mind that injustice may easily be done to theories by forcing them into some particular classification because some common form of language is employed in them, without careful consideration of the real meaning of the language and of other essential principles which the theories comprehend. CHAP. III. SECT. I. § 42. Amongst those who study the process of Philosophical perception from the second, which we called method. the philosophical, stand-point there are important differences. They all begin by giving up the position of practical dualism which is the result of the ordinary education of the organism through which CHAP. III. every one passes. They analyse the objects of the senses into materials given in consciousness, and endeavour to ascertain those facts of consciousness which are irreducible to others more simple. Taking up their position, thus, at the origin of knowledge, they work their way outwards, tracing the process by which knowledge is gradually acquired. The principal differences which exist between different theories of this class arise from the different views which are taken regarding the nature and significance of the facts revealed in consciousness. As in the previous class we hesitated to attempt giving a more minute classification of the theories contained in it for fear of doing injustice to some of them, so now it will be as well to postpone minuter description until we have examined the important theories which assume this stand-point. Our general division of theories of perception into two great classes has been instituted chiefly for the purpose of furnishing a sort of key to the understanding of the theories to be passed in review. We shall not examine all the theories of each class in immediate succession, but shall rather take them in the historical order of their appearance, being thus better able to perceive their relations to one another. CHAP. III. SECTION II. DESCARTES. Descartes' founda § 43. Descartes began his philosophising by resolving to doubt the truth of all propositions received tion. at second-hand. He found himself able to doubt the existence of the world, of God, of his own body, of everything, in short, except doubt itself. But doubt is only a form of thought, and hence, according to Descartes, the act of thinking itself, as given in consciousness, was the one certain foundation of all knowledge. But the assertion of thinking involves the assertion of a thinking being; cogito ergo sum. Thinking, in its widest sense, is the essence of mind. Deity. Having thus established a firm foundation on which to build the superstructure of his system, Descartes proceeded to prove the existence of God. According Proof of a to him, "When the mind reviews the different ideas that are in it, it discovers what is by far the chief among them that of a Being omniscient, all powerful, and absolutely perfect; and it observes that in this idea there is contained not only possible and contingent existence, as in the ideas of all other things which it clearly perceives, but existence absolutely necessary and external . . . so from its perceiving necessary and external existence to be comprised in the idea which it has of an all-perfect Being, it ought manifestly to conclude that this allperfect Being exists.” * *Principles,' part i., xiv. |