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THE PRINCIPLE OF LEAST ACTION, ETC. 4<)M devices, e.g., determinants, and finally calculating machin.-s are all devised in the spirit of this conviction. 1 As regards Mach's general position in this matter, while we must allow the truth of the fact that ' Physics is experi- ence arranged in economical order,' 2 we do not consider that he has touched the heart of the matter when he says that 'the goal which physical science has set itself is the simplest and most economical abstract expression of facts '. 3 We should be much more inclined to agree with Descartes in making an essential point of the deductive method of inquiry and laying only subordinate though still very strong emphasis on the necessity of economy. 4 And this is to give continuity the primacy over economy. With Avenarius 5 the principle of economy, or, as he puts it, the principle of least expenditure of force, is the guiding principle of Philosophy. It is (1) the principle from which philosophy springs, i.e., in pursuing that principle into its consequences we are led to Philosophy, and further, led to Philosophy of a certain kind, for (2) it is the principle which determines the central problem of Philosophy, the attempt to unify the world under one general concept; (3) it is the principle which, rigidly carried out, determines the structure of Philosophy ; and (4) it is the principle which inspires the methods of Philosophy. 6 The characteristic of philosophic thought that brings it thus under the law of economy is its essentially conceptual nature. By this is meant specifically the subsuming of presentations under general notions, and, more generally, the apprehension of the unknown in terms of the known. The latter process is characteristic of all apperception what- soever, the former, in its fulness, of Philosophy only, for it is only Philosophy that carries the process of subsumption to its natural issue, it is only Philosophy that seeks to bring 1 Mach, id., pp. 487, 488. 2 Ibid., id., p. 197. 3 Ibid., id., p. 207. * Cf. Regulse, xiii., xiv., xvi., xviii., xx. 5 Philosophic als Dt.nken der Welt nach dem Princip des kleinsten Kraftmaases, Leipzig, 1876. A brief but excellent summary of this treatise can be found in MIND O.S., vol. i., p. 298 ; it is also summarised and discussed at greater length in a leading article of the Literarisches Centralblatt, 15 (1876) ; ef. also Revue. Philoxophique, 3" Annee, p. 216. 6 Cf. Avenarius's own introduction to his Critique of Pure Experience. It is a significant fact that the principle of economy which so dominates the Prolegomena should be completely ignored in the C?it!i/u, itself. The inference is that in serving the abstract office of a ' Leitfaden ' or guiding clue to the most economical conception of experience its real value had been exhausted, but this, of course, is not the meaning of Avenarius in dealing with the principle.