228 M. W. CALKINS : important and fruitful category of the external world, and not an especially emphasised category of the inner life ; they do not in the least disprove that the causal is a possible way of regarding the psychical experience. 1 On the other hand, in so far as the psychical experience is viewed as unquestionably it may artificially be viewed as made up of a series of single states in so far it must be subject not merely to categories of significance, but to phenomenal categories, including those of universal connexion. This view is strengthened by the ordinary doctrine that time is a category of the inner life, and it cannot be disproved by the assertion, even if substantiated, that we actually come to the conception of internal causality through the previous observation of physical causation. So long as mental facts may be regarded as necessarily connected, each with each, so long causality is a psychical as well as a physical category. Therefore a hypothetical solitary individual, without con- sciousness of other finite selves, and hence without con- sciousness of externality, might think of his consciousness as made up of isolated and independent units. These units would have gained their permanence, probably, through repetition ; the necessary connexion would have been suggested by repeated experiences in the same order. With physical causality, however, that is, with the appli- cation of this conception of necessary connexion to events regarded as common experience of all possible subjects, one enters the sphere of the universal and the describable, and there is introduced at once the possibility of verification through experiences which are readily repeated, imitated and communicated. Through such verification the empirical causal propositions arise, the assertions that such and such an event has such and such a cause. This is the sort of doctrine of causality which Hume's criticism really touches, and he is quite correct, of course, in his conclusion that necessity never can be predicated of any observed connexion, and that the persuasion of empirical necessity is an effect of habit. But the assertion of this or that cause has no relation to that fundamental universality of causal con- nexion expressed in the proposition : " Every event has a 1 Cf. Hume, who, though he usually treats causality as connexion of outer events with each other (or of psychic facts with the 'real objects ' which he inconsistently assumes), nevertheless, says distinctly (Treatise, bk. i., pt. iii., 2, end) that the ideas of cause and effect are " derived from the impressions of reflexion, as well as from those of sensation. Passions are connected with one another ... no less than external bodies are connected together."
