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cal hypothesis that is, an attempt to assign a meaning to Reality, or fill in the conception of it to a certain. limited extent. We have seen that Psychology, arising from the subjective reference of knowledge, may be distinguished as a subjective science, the others as objective sciences. In this case, 'Psycho-physics' or 'Physiological Psychology' must be placed among the objective sciences; when Psychology devotes itself to experiment—that is, chiefly, to physiological experiment-it simply places itself at the standpoint of the sciences of non-human nature: "it is as purely objective as it was before purely subjective; it takes its stand in the object from the outset, and treats subjective facts themselves as objective-i.e., as mere appendages or accompaniments of the objective facts of nerve and brain."

This brings us to notice that the hypotheses of the sciences may be arranged in an order of decreasing generality and increasing complexity. Chemical processes involve mechanical processes, but cannot be reduced to the latter; biological processes involve chemical and mechanical processes, but cannot be reduced to either of the latter. What then is to be said of the relation of Biology and Psychology? Our conclusion must be that truth is on the side of those psychologists who defend what is called the 'causal interaction' of mind and brain, in the sense that the energy of consciousness in some way conditions the state of the brain, while the latter in some way conditions conscious states. It is obvious from what has been said that no physical or mechanical law, such as that of Conservation of Energy, can be brought in as evidence in this matter. The principle of Conservation can only be made applicable to the case by assuming

that the animal organism forms part of, and is merely a part of, a closed system of mechanical movement, which is the material universe as a whole. The fact that this assumption is actually dallied with by many physiological psychologists and popular apostles of science need not deter us from recognising that it is simply a wild dogma. The real question is, Has Extension an existence of coequal validity with that of Consciousness? Descartes, Spinoza, and the modern 'monists' assume, without proof, that it has; but this is entirely a metaphysical question, which cannot be settled by a dogmatic assumption.1 It is on 'phenomenological' grounds that we reject the monistic or identity hypothesis, as expounded, for instance, in Höffding's Outlines of Psychology. We may express the relation as before: psychological processes 'involve' physiological, but cannot be reduced to the latter. But there is a very important difference. We found that chemical changes involved' mechanical, and could not be reduced to the latter; but it seemed that the only scientific treatment of these changes consists in the analysis of their mechanical conditions,-of course, with the recognition that these are only conditions, and that the whole process is more than they: the result being that we can only give an external descriptive account of the qualitative changes which are the manifestation of the 'more'-of what transcends mere mechanism in the process. The case seemed to be the same with regard to the mechanical and chemical conditions of the changes in which life consists. But it is not the case that the only scientific treatment of consciousness consists in the analysis of its physiological conditions, although psychologists are more ready to acknowledge

1 On this whole subject, see Appendix to this chapter.

this in a general way than to act upon it in particular cases.1

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The function of Epistemology is explicitly to formulate and compare the ontological assumptions on which the several sciences rest. It has to "submit such conceptions to a critical analysis with a view of discovering how far they can be thought out, or how far when this is done they refute themselves and call for a different mode of statement if they are to be taken as a formulation of the ultimate nature of the real." This might be called a 'criticism of categories.' The investigation is 'critical,' because it is not content with mere phraseology or mere picture-thinking, but with clear and distinct meanings. Under these circumstances it appears that Reality cannot be conceived except after the analogy of our own conscious and self-conscious life-or after the analogy of some aspect of that life, such as unity or identity. It is a question whether reality conceived in any other way does not become an existence without content: in other words, does not approximate to that conception of empty or abstract Being which as a conception is indistinguishable from Nothing. From this point of view, if we regard reality as an all-inclusive whole which is implicitly 'filled in '-of which the general nature is implicitly but fully known-from the outset (by reference to the conscious life of man), then we may say that the sciences make abstractions of particular portions of it. For this way of envisaging the matter, a proper use of the

1 For a very careful examination of the extent to which Physiology can aid Psychology, see Mr Stout's Analytic Psychology, vol. i. Introduction, § 4.

2 Cf. Enc. Brit., art. Philosophy, p. 793a.

Hegelian Logic is most helpful.1 Epistemology has further to investigate and state clearly the methodological assumptions made by the special sciences. Among these the most important are: the Uniformity of Nature," the same system of conditions, if it occurs more than once, will produce the same effect"; and Universal Causation,-" every process or fact must be somehow completely conditioned by other processes.' In examining these, we are led to inquire into the nature of rational evidence and proof, and into the different kinds of evidence approximate to the different special sciences. It is most important to know what kind of evidence we ought reasonably to expect in an investigation belonging to a particular science. These questions have their centre in the idea of a 'hypothesis' as explaining perceived facts, and of the method by which we pass from the facts to the explanation,— in other words, from empirically valid to unconditionally valid Judgments. Under what conditions is this possible? These are the problems with which what has been called Inductive Logic' has professed to deal; and we may safely say that its achievements have been in inverse proportion to the magnitude of its pretensions. This can hardly be a matter for surprise, seeing that our one great authoritative text-book of Inductive Logic-or what until recently was such— implies a theory of Knowledge or Nescience which is in part based on the agnostic sensational empiricism of Hume. I do not deny that Mill's philosophy leaves room for physical science, if by the latter is meant nothing more than a classification of 'actual or pos

1 See Mr M 'Taggart's Studies in the Hegelian Dialectic, ch. i. §§ 20-24; ch. ii. § 34; ch. iii. §§ 87-90.

sible' phenomena according to their resemblances and differences, and a codification of their orders of coexistence and succession: though it would be difficult to adapt this view of physical knowledge to the actual extent and significance of such sciences as Physics and Chemistry. On the other hand, even a 'positivism' of this kind is excluded by the principles developed in Hume's Treatise of Human Nature. The difference between Hume and Mill in this respect is due to the fact that, for the former, the fleeting impressions and ideas of the moment are the only reality; while the latter introduces what is in effect the objective world of science and common-sense, in the guise of 'permanent possibilities of sensation.' But, like all 'positivists,' he limits the categories of the world - that is, the principles to be used in rationally interpreting it, in gaining scientific knowledge of it to those of "the like and the unlike, the synchronous and successive": and thereby reduces his Theory of Knowledge to an incoherent fragment.

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§ 6. The problem of Ontology consists in the coordination of the results of the special sciences with each other. Its ultimate ideal is to connect all parts of our knowledge together in an organically complete whole the more we are able so to connect them, the truer for us is their account of reality. In this sense, the ultimate test of truth is consistency or harmony: the 'ultimate' test, in distinction from the test which applies to Judgments of perception, referring to what is true at a particular time and place only. Our knowledges are the more true, the more they mutually support one another. This has been already illustrated and defended in relation to those principles which we

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