[Footnote 80: Our comparison does no more than develop the content of the term [Greek: logos], as Plotinus understands it. For while the [Greek: logos] of this philosopher is a generating and informing power, an aspect or a fragment of the [Greek: psychê], on the other hand Plotinus sometimes speaks of it as of a _discourse_. More generally, the relation that we establish in the present chapter between "extension" and "detension" resembles in some aspects that which Plotinus supposes (some developments of which must have inspired M. Ravaisson) when he makes extension not indeed an inversion of original Being, but an enfeeblement of its essence, one of the last stages of the procession, (see in particular, _Enn._ IV. iii. 9-11, and III. vi. 17-18). Yet ancient philosophy did not see what consequences would result from this for mathematics, for Plotinus, like Plato, erected mathematical essences into absolute realities. Above all, it suffered itself to be deceived by the purely superficial analogy of duration with extension. It treated the one as it treated the other, regarding change as a degradation of immutability, the sensible as a fall from the intelligible. Whence, as we shall show in the next chapter, a philosophy which fails to recognize the real function and scope of the intellect.] [Footnote 81: Bastian, _The Brain as an Organ of the Mind_, pp. 214-16.] [Footnote 82: We have dwelt on this point in a former work. See the _Essai sur les données immédiates de la conscience_, Paris, 1889, pp. 155-160.] [Footnote 83: _Op. cit._ chaps. i. and ii. _passim_.] [Footnote 84: Cf. especially the profound studies of M. Ed. Le Roy in the _Revue de métaph. et de morale_.] [Footnote 85: _Matière et mémoire_, chapters iii. and iv.] [Footnote 86: See in particular, _Phys._, iv. 215 a 2; v. 230 b 12; viii. 255 a 2; and _De Caelo_, iv. 1-5; ii. 296 b 27; iv. 308 a 34.] [Footnote 87: _De Caelo_, iv. 310 a 34 [Greek: to d' eis ton autou topon pherethai hekaoton to eis to autou eidos esti pheresthai].] [Footnote 88: On these differences of quality see the work of Duhem, _L'Évolution de la mécanique_, Paris, 1905, pp. 197 ff.] [Footnote 89: Boltzmann, _Vorlesungen über Gastheorie_, Leipzig, 1898, pp. 253 ff.]