The fact is that there are two sorts of unobjectionable psychology, neither of which describes a mechanism of disembodied mental states, such as the followers of Locke developed into modern idealism, to the confusion of common sense.[8] One unobjectionable sort of psychology is biological, and studies life from the outside. The other sort, relying on memory and dramatic imagination, reproduces life from the inside, and is literary. If the literary psychologist is a man of genius, by the clearness and range of his memory, by quickness of sympathy and power of suggestion, he may come very near to the truth of experience, as it has been or might be unrolled in a human being.[9] The ideas with which Locke operates are simply high lights picked out by attention in this nebulous continuum, and identified by names. Ideas, in the original ideal sense of the word, are indeed the only definite terms which attention can discriminate and rest upon; but the unity of these units is specious, not existential. If ideas were not logical or aesthetic essences but self-subsisting feelings, each knowing itself, they would be insulated for ever; no spirit could ever survey, recognise, or compare them; and mind would have disappeared in the analysis of mind. These considerations might enable us, I think, to mark the just frontier of common sense even in this debatable land of psychology. All that is biological, observable, and documentary in psychology falls within the lines of physical science and offers no difficulty in principle. Nor need literary psychology form a dangerous salient in the circuit of nature. The dramatic poet or dramatic historian necessarily retains the presupposition of a material world, since beyond his personal memory (and even within it) he has nothing to stimulate and control his dramatic imagination save knowledge of the material circumstances in which people live, and of the material expression in action or words which they give to their feelings. His moral insight simply vivifies the scene that nature and the sciences of nature spread out before him: they tell him what has happened, and his heart tells him what has been felt. Only literature can describe experience for the excellent reason that the terms of experience are moral and literary from the beginning. Mind is incorrigibly poetical: not because it is not attentive to material facts and practical exigencies, but because, being intensely attentive to them, it turns them into pleasures and pains, and into many-coloured ideas. Yet at every turn there is a possibility and an occasion for transmuting this poetry into science, because ideas and emotions, being caused by material events, refer to these events, and record their order.