214 HOWARD V. KNOX: Pearson has a perfect right, if he chooses, to use the word " description " in the sense in which every one else uses the phrase " causal explanation " : l but he would have done better to inform us that it is to the sound and not to the sense of " explanation " that he takes exception. II. Any treatment of the question of externality would be in- complete if it did not include some notice of the theory (alluded to on p. 206 and p. 210) that in thinking and speak- ing of material things and events which are not actually objects of perception, we mean merely that on fulfilling the appropriate conditions, those things or events " would be perceived ". 2 For the sake of reference I will call this theory Apologetic Idealism, since it plays so large a part in attempted reconciliations between idealism and science. We have now to consider whether this theory will hold good iu face of the leading results arrived at in part i. First of all, it must be noticed that Apologetic Idealism is obviously intended to provide a substitute for the idea of uuperceived existence ; in the sense that it seeks to reduce this idea to lower terms, so to speak. Therefore the " conditions " it speaks of must be mental conditions (i.e., pure modifications of consciousness), and must not be conceived as appertaining to the external world : other- wise, we shall have re -introduced the original idea of unperceived existence, and thus completely stultified our- 1 See, e.g., footnote on p. 312 of The Grammar of Science: "As every external perception is a group of sense-impressions, and as our senses are limited, the atom, if a real phenomenon, could only appear sensible by colour, hardness, temperature, etc., the very sense-impressions it is conceived to describe. Hence, if the atom is to be not these things but their source, it may be truly termed imperceptible." Though this passage is not particularly luminous even if the word "explain" is substituted for the word " describe " in it, it is in still worse case if we do not effect this substitution. Professor Karl Pearson fails to see that even if we discard ' efficient causes ' there is still a useful distinction between description and explanation. As it is, he leaves the origin of the fallacy of efficient causes quite unexplained. 2 This special theory has to be distinguished from the general theory, which is not here made an object of attack, that all experience can be resolved into subjective elements, which fact indeed is obvious, seeing that "subjective" = " forming part of experience ". My argument, in fact, is not that experience cannot be expressed in subjective terms ; but, that it cannot be reduced to subjective laws, pure and simple. There cannot be such a thing as a pure science of mind, free from all admixture of physical science.
