however, this second stage of the problem of Perception is of little or no philosophical importance; and at any rate the line of demarcation between inference and immediate judgment are not very well defined. It is essential that extension, and consequently, a reality opposed to the unextended subject of consciousness, be directly presented, but granted such an immediate perception, even limited to the spatial character of my own material organism, our knowledge of the rest of the universe would be readily built up.3

HISTORICAL SKETCH OF MODERN THEORIES OF EXTERNAL PERCEPTION.

The question of External Perception has played such a large part in modern philosophical speculation that we deem it expedient to attempt a brief sketch of the subject. And we do this all the more willingly because experience has assured us that here, as often elsewhere, the most convincing proof of the true doctrine is to be found in a careful examination of the history of counter-hypotheses.

Descartes (1596-1650), whose philosophical speculations start from the dictum that I have an immediate and infallible knowledge of my own thought and of nothing more, may be justly considered the author of the problem of the bridge from the mind to the material world. It is to Locke (16321704), however, that the various forms of British scepticism, together with the Idealism of Kant, are to be traced. Knowledge, Locke repeatedly maintains, consists in the perception of agreement or difference between our ideas. We thus immediately apprehend not an external reality, but our own

3 Thus Hamilton justly observes: "It is sufficient to establish the simple fact, that we are competent, as consciousness assures us, immediately to apprehend the Non-Ego in certain limited relations; and it is of no consequence whatever, either to our certainty of the reality of the material world, or to our ultimate knowledge of its properties, whether by this primary apprehension we lay hold, in the first instance, on a larger or a lesser portion of its contents.' (On Reid, p. 814.)

mental states. Nevertheless, Locke holds that a material world does exist outside of the mind. He is thus a Hypothetical Dualist. We only know psychical representations, but we posit as their cause a physical universe.

Bishop Berkeley (1685-1753) soon made manifest the inconsistencies of Locke's teaching. Berkeley is celebrated chiefly for two contributions to the history of Philosophy, his system of Phenomenalistic Idealism and the Theory of Vision known by his name. The essence of the latter is contained in the two tenets that the eye of itself can perceive neither (a) distance, nor (b) surface extension. Visual sensations had originally as little reference to space as sounds or tastes. By experience and association, the sensations of the eye grow to be symbols of tactual and motor sensations, which constitute our knowledge of solid bodies, and of space of three dimensions. From this account of the psychology of perception the transition to his metaphysical theory of the nature of the External World is easy. Locke's groundless assumption that we can immediately perceive nothing but our own mental states, is accepted without question. All objects of knowledge are held to be reducible to ideas of the senses (sensations), internal feelings such as emotions, and acts of the imagination. Accordingly, we may not assert the existence of an independent extra-mental world. We can know or perceive only what is in the mind. The esse of every knowable object is percipi. If material substances existed beyond consciousness, they could in no way be like our ideas, and cognition of such things by ideas would be impossible. Moreover, matter could not act upon an unextended spirit. Therefore the hypothesis of an inert corporeal world which has existed for a time unperceived must be abandoned. Still, Berkeley vigorously asserted that his theory is in complete harmony with the belief of mankind. The table, chair, or fire, which I perceive, he does not deny to exist; but, adhering to Locke's assumption, he calls whatever is apprehended an idea, and going still further he repudiates the hypothetical material cause supposed by his master to have awakened these ideas. But whence then do these ideas come, and what happens when I cease to perceive them? Berkeley replies that God, and He alone, is the cause of my ideas. By the Divine agency, and not by any hidden inconceivable material substance, the permanence, regularity, and orderliness of the ideas are sustained. When I no longer think of ideas (material objects) they still endure in the Divine mind, and may be apprehended by other men. In Berkeley's system,

then, there are held to exist minds or spiritual substances,. ideas, and the Divine spirit.4

David Hume (1711—1776), similarly starting from Locke's principles, pushed Berkeley's Idealism to the most absolute scepticism. All cognitions, or all objects of cognition-for with these writers the terms are interchangeable-arereducible to impressions (sensations) and ideas, fainter copies of the former. To explain our belief in a permanent external reality, as well as to account for our other fundamental convictions, Hume appeals to the laws of the Association of Ideas. Through "custom" by the reiterated occurrence of various impressions we grow to believe in the enduring existence of material things when unperceived. Such belief is, however, an illusion; we only know the transient mental impressions. There is no such thing anywhere as an abiding substance, the substratum of changing qualities or accidents.. We have no "impression " of it, therefore it does not exist. Berkeley got thus far as regards the notion of material substance; but Hume logically shows that by the same reasoning the idea of a spiritual substance, of a permanent mind amid changing states of consciousness is equally fictitious and unreal. The mind, just as well as the material world, is nothing more than a cluster of transitory impres-sions. The persuasion that nothing can begin to exist without a cause is also due to association. No single experience could give us the idea of causation; but the frequent repetition of two successive impressions so welds them together in our minds that we are deluded into the belief of some mysterious causal knot binding them, while there is really no connexion but that of succession. This illusory belief in particular instances of causality is afterwards gradually widened into the universal law, that every being which begins to exist presupposes a cause.

We have here all the essentials of later associationism. The substantial souls, retained by Berkeley, follow the material world of Locke, and the Divine Spirit also becomes a useless

4 Berkeley's theory may be objected to on various grounds, such as his equivocal use of the terms idea and conceive, and his unquestioning acceptance of Locke's assumption, but we have never. seen any experiential argument which, strictly speaking, disproves the hypothesis of hyperphysical Idealism. God, without the intervention of a material world, could potentiâ absolutâ immediately produce in men's minds states like to those which they experience in the present order. The only demonstrative argument against the Theistic Immaterialist is, that such a hypothesis is in conflict with the attribute of veracity which he must ascribe to the Deity.. God could not be the author of such a fraud.

and inconceivable hypothesis. Hume, too, possessed the merit of realizing clearly and frankly admitting, what subsequent disciples of sensism either fail to see, or attempt to ignore, that the groundwork of physical science, and the certainty and exactness of mathematics are fatally destroyed by consistently following out the assumptions of the school. The conclusions of the Scotch sceptic thus constitute a complete reductio ad absurdum of Locke's principles.

7. Stuart Mill and Dr. Bain.-The chief modifications introduced into the general theory by more recent sensationalists, are the final dismissal of Berkeley's hypothesis of the Divine action, the greater importance assigned to the muscular sense, and a more elaborate attempt to harmonize the new conception of the external world with ordinary beliefs. However, the arguments are in the main similar in kind to those urged by the earlier advocates. Thus, it is asserted, that a world existing independently of the mind is inconceivable. "To perceive is an act of the mind. . . . To perceive a tree is a mental act; the tree is known as perceived and not in any other way. There is no such thing known as a tree wholly detached from perception, and we can only speak of what we know." Consequently, the hypothesis of an external world existing when unperceived is absurd. "The prevailing doctrine is that a tree is something in itself apart from all perception; that by its luminous emanations it impresses our minds, and is then perceived, the perception being the effect of an unperceived tree the cause. But the tree is known only through perception; what it may be anterior to or independent of perception we cannot tell; we can think of it as perceived but not as unperceived. There is a manifest contradiction in the supposition, that we are required at the same moment to perceive the thing and not to perceive it."5

5 Dr. Bain, Mental Science, pp. 197, 198. In Emotions and Will (3rd Edit.), p. 578, he still denies that "the situation intimates anything as an existence beyond consciousness." This argument in the hands of Dr. Bain, as in those of Berkeley, is based on a deceptive ambiguity in the terms "conceive" and "perceive." We cannot of course perceive an unperceived world, nor can we conceive a world the conception of which is not in the mind; but there is no contradiction or absurdity in the proposition: “A material world of three dimensions has existed for a time unperceived and unthought of by any created being, and then revealed itself to human minds." Dr. Bain's description of the prevailing doctrine" is only applicable to the theory of mediate perception. It does not refer to Natural Realism, which makes the external material reality the perceived and not the unperceived cause of our cognitions.

6

The chief strength, however, of the theory lies in the asserted sufficiency of the account which it professes to give of the material world apprehended by us. Assuming as self-evident the axiom that we can know only our own ideas, the external universe, it is alleged, really means to us nothing more than certain sensations plus possibilities of other sensations. The most objective and real attributes of material things are in common belief their extension and impenetrability. Nevertheless, these properties, it is asserted, are ultimately reducible to groups of muscular feelings possible and actual. "The perception of matter, or the object consciousness, is connected with the putting forth of muscular energy as opposed to passive feelings. Our object consciousness farther consists of the uniform connexion of Definite feelings with Definite energies. The effect that we call the interior of a room is in the final analysis a regular series of feelings of sense related to definite muscular energies. A movement one pace forward makes a distinct and definite change in the ocular impressions; a step backward exactly restores the previous impression. . . . All our so-called sensations are in this way related to movements. . . . On the other hand, what in opposition to sensations we call the flow of ideasthe truly mental or subjective life-has no connexion with our movements. We may remain still and think of the different views of a room, of a street, of a prospect in any order. "7

...

The apparently independent world of every-day experience has not suddenly manifested itself to us after the manner of a transitory hallucination. It is a gradual growth, and it is in tracing the supposed genesis of this illusory belief that Mill best exhibited his psychological and metaphysical ingenuity. Starting with the postulates of expectation, the occurrence of impressions, and the laws of mental association, he professes to satisfactorily explain all our present convictions. We experience, he says, various sensations, such as those of colour, sound, and touch. After they have passed away we conceive them as possible. These feelings usually occur in groups, thus the consciousness of yellow is found in combination with certain sensations of contact, of smell, and of taste, which go to make up our perception of an orange. 6 It should be carefully borne in mind that in the associationist theory a possibility of sensation" is not a real actual agent existing out of consciousness. It is as such, non-existent. Its only existence is in the idea or conception by which future experiences are represented. Mill seems frequently to forget this.

7 Mental Science, pp. 199, 200.