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COMPARATIVE] would be found intelligible as well. Psychophysical parallelism, then, we conclude, is not a philosophically tenable position; and—pending the metaphysical discussion as to the ultimate nature of interaction generally—we have to rest content with the second of the three possible modes of connexion above defined, as occasional ism formulates it. According to this, the two series, the psychical and the physical, are not independent and “closed” against each other; but in certain circumstances—e.g. in perception—physical changes are the occasion of psychical, and in certain circumstances—e.g. in purposive movements—psychical changes are the occasion of physical: the one change not being explicable from its psychical antecedents, nor the other from its physical.

Into the metaphysical discussion we cannot, of course, enter here. It must suffice to say that it will not be conducted on the lines of our present inquiry: it will not start from a dualism of matter and mind, either regarded as substances or as phenomena. Its problem will rather be the interaction of subject and object—a duality in the unity of experience, which by no means coincides with the dualism of matter and mind, neurosis and psychosis, and the like.

48. Psychoneural parallelism is no doubt a well established generalization; nevertheless, concerning its exact range and its precise meaning there are differences of opinion. It is applicable, every one will allow, so soon as there is evidence of experiences individually acquired (cf. § 3); and from such point onwards, in ascending any biological phylum, we find that the psychical and neural aspects differentiate and develop together. But how when we descend? Interpreting the neural correlate physiologically, and not morphologically, as referring primarily to function and not to structure, we find that even in unicellular organisms it is still present as irritability and conductivity (leading to contraction, secretion, &c.). But as at higher levels psychosis is correlative to neurosis, the principle of continuity would seem to justify us in assuming a like correspondence here. Moreover, “learning by experience,” the comparative psychologists criterion, obviously presupposes some antecedent and underlying process, of which it is the differentiation and development. And our general analysis of mind, if correct, enables us to describe this process—“the irreducible psychical minimum,” of which we are here in search. We have such complete psychosis—and it is the simplest we know—in the emotional or diffused movements that follow immediately upon sensation; and these are so far purposive—though not intentional—that they tend to heighten or retain what is pleasurable, and to alleviate or remove what is painful. Given that plasticity, which is the psychological presupposition of all acquisition, then learning by experience is a possible development from such a primitive stage.

But though every psychosis have its concomitant neurosis, it is uncertain how far the converse holds good. The action of the heart, for example, depends upon neuroses of which we have now no direct consciousness. Facts of this kind have led to three hypotheses concerning the lowest forms of life, differing more or less from that just proposed. (i.) Perfectibility and instinct are found, it is said, to be in inverse ratio. Hence in the lowest forms of life there is no “learning by experience,” because a stationary state of complete adjustment to environment has been already attained, and all reactions have therefore become “secondarily automatic”: consciousness, having served its purpose, has disappeared. To such a very Buddhistic psychology it may be objected: (1) that even organic refiexes tell upon the so-called vital sense or coenaesthesis, and so far—the irreducible minimum being still intact—do not preclude all possibility of learning, should occasion arise; and (2) that the psychical life, even of a Protozoan, does not, according to the best evidence, show any such mechanical finality as is here supposed. (ii.) According to the second view, which is advocated by Herbert Spencer, the behaviour of the lower organisms is wholly made up of such reflexes, supposed to be devoid of all psychical concomitants; but consciousness—so far from having disappeared—first comes upon the scene at the opportune moment when the increasing complexity of the mechanism calls for its guidance. Psychologically this hypothesis is less defensible than the last, and it has already been dealt with at some length (cf. § 7). It not only assumes, as that does, far more uniformity in the interaction of organism and environment than the facts warrant, but in regarding life as prior to mind, and as the means of its evolution, it burdens science with two insoluble problems instead of one. For even if it were possible chemically to build up protoplasm, we should still be as far from organisms as a heap of bricks are from putting themselves together as a house. (iii.) The last view we have to notice is essentially an extension of the preceding, and is chiefly interesting as a reductio ad absurdum of that. The physics of colloidal substances—at present wanting, but confidently expected “in the near future” by certain biologists—is the key which is to unlock the mysteries of protoplasm. Certain organisms, regarded as varieties of such a substance, react positively to a given physical property of the environment, and others negatively: thus a moth flies towards the light, and a centipede runs from it—the one is positively, the other negatively, “heliotropic”; the radicle of a seed, growing downwards, is, positively, the plumule, growing upwards, is, negatively, “geotropic.” Instincts are but complexes of such tropisms, and owe their character entirely to the symmetrical form and definite structure of the colloidal substance. Now if it facilitate the work of the biologist to say that when what we ordinarily regard as a hungry caterpillar climbs to the tip of a branch it is forced so to do by positive heliotropism; that then positive chemiotropism sets up mastication of the young buds; and that, lastly, “we can imagine this process leading to the destruction of the substances in the skin of the animal that are sensitive to light, and upon which the heliotropism depended,” so leaving it free to crawl downwards and come in contact with the new buds which have in the meantime unfolded —if such language serve any useful purpose, all well and good; only it must be applied to the hungry man too: in short, all behaviour must be described in the same terms. For the champion of colloids to betake himself to consciousness as he approaches the higher forms of life is as much a breach of methodological parallelism as it is for the psychologist to fall back upon protoplasm as he approaches the lower. But to suppose that psychical processes first appear in the complicated form of association of ideas—which learning by experience is taken to imply—and at the same time to assume that such experience, even when it appears, is “ultimately due to the motions of colloidal substances,” these are incongruous absurdities which only the grossest ignorance would be bold enough to maintain.

Concluding, as we have done, that mind and matter—as we may provisionally call them—do really interact, we naturally infer that organic structures are not the result solely of material processes, but involve the co-operation of mental direction and selection: in other words, we are led to regard structure as partly shaped and perfected by function, rather than function as solely determined by structure, itself mechanically evolved. And such a view is justified by the fact that mechanical evolution is primarily a process of “degradation” rather than development, a case of facilis descensus contrasting with the upward struggle of life per aspera ad astra. Still, the notion of life or mind as formative and directive has its difficulties. In the first place, we have no experience of mind organizing matter-no experience of the actual process, that is to say-however sure we may feel of the fact. Hence the occasionalism to which here, at any rate, science is confined. But even so, the difficulty is not wholly removed. In the handicrafts whence we derive the conception