And in this investigation no special weight will be laid upon the question whether the sense-quality apprehended is a char acteristic belonging to physical things or merely a way in which physical things appear to us to be characterised. Or, take what is called a belief. The aim of the psychologist will be to exhibit the antecedent mental conditions that led to its being enter tained, how it is related to the emotional and volitional sides of the mental life in question, with what states of the bodily organ ism ism t is connected, and so on. But obviously there remains a characteristic set of problems which this psychological treatment of cognition leaves entirely untouched. The act of perception pur ports to give what is called knowledge of the external world. In entertaining a belief, the conscious subject is persuaded of its truth, that is to say, that it corresponds to something that is real and independent of the act of believing.
This contrast between the existence in an individual mind of a state or act of knowing and the significance of what is contained therein—the contrast between knowing as a psychical occurrence and knowledge as representative of relations in the material known—presses upon us whatever portion of cognitive activity be selected, whether perceiving or imagining or thinking. How is it possible that in and through means of a subjective act there should be awareness of what is, ex hypothesi, distinct both from the act and from the mind of which the act is a transitory phase? Again, from the nature of a cognitive act, as the psychologist describes it, it is evidently possible that it may fail to accomplish its natural end, the attainment of truth; its content may not cor respond to fact. We are, therefore, driven to ask, under what conditions and in what forms is such a correspondence to be ob tained, when and where can we be reasonably assured that our representation of the real is true? Such questions are manifestly of a different order from those which have been designated psy chological, and, without going to the extent of saying that in the attempt to answer them psychological considerations are alto gether irrelevant, it may safely be asserted that they are insuffi cient. The worth or significance of knowledge can never be de termined by tracing the stages of its history.
The difference between the two points of view was indicated by Locke. In the Introduction to the Essay, Locke gives a pre liminary statement of the subjects with which he proposes to deal in the second and fourth Books. "First," he writes, "I shall inquire into the original of those ideas, notions, or whatever else you please to call them, which a man observes, and is conscious to himself he has in his mind; and the ways whereby the under standing comes to be furnished with them." This is a psycho logical inquiry. He proposes to try to find out what the cognitive states of the individual mind are, which of them are complex and which simple, and to analyse the former into their constitu ents. Furthermore, he proposes to trace the genesis and develop ment of cognition, and the way in which it gradually comes to be what we find it to be in ourselves. But he proceeds : "Secondly,
I shall endeavour to show what knowledge the understanding bath by those ideas, and the certainty, evidence and extent of it." This is, in brief, the subject-matter of epistemology. He proposes here to try to find out how by means of our mental states we obtain information about the world in which we are, how far that information is reliable, and the degree to which we are justi fied in placing credence in it.
Unfortunately, however, although he had thus shown himself to be aware that these two lines of inquiry are different, Locke, in his subsequent procedure, is constantly confusing what he had carefully distinguished, and drawing upon considerations which properly belong to one of these sets of problems in dealing with the other. It was in Kant's Critique of Pure Reason that the methods and aims of epistemology were first definitely formulated, and in which it was exhibited as the mode of approach to the other problems of philosophy. More than once Kant lays em phasis upon the consideration that the first part of the Critique would be misconstrued if regarded as a treatise on the psychology of cognition. The question with respect to knowledge which it was concerned to answer was the question quid juris and not the question quid facti, the question as to the validity of knowledge and not the question as to the natural conditions under which knowledge grows up in the individual mind. Taking for granted that knowledge is possible, Kant seeks to show how it is possible, to inspect it in its character as apprehensive of fact and to deter mine the conditions implied in its nature. Empirical psychology seemed to him to stand related to this "critical" inquiry in much the same way as the natural sciences stood related to it. It involved in its methods of research presuppositions which it was the business of a theory of knowledge to examine, and it em ployed notions which it was the business of a theory of knowledge to criticise. Psychology begins by assuming that the world of experience can be broadly divided into two realms of f acts,— those which it is customary to call outer and inner, objective and subjective,—and all its explanations are based upon the mutual interconnection of these.
But from the point of view of a critical theory of knowledge, the division between outer and inner, between objective and sub jective, itself demanded investigation and defence. The meaning of such a distinction for the conscious subject within whose ex perience it presents itself called for consideration, and the con ditions under which it is recognised by him required to be shown. Or, in other words, knowledge exhibits the two characteristic features—reference to a self that knows and reference to a reality other than self ; and the former is no less a problem than the latter. It has to be confessed that Kant was not always successful in keeping his own treatment within the limits he had prescribed; but it was he who first fully realised the import of the problems that fall to a theory of knowledge.