When the opinions of the Sensational School had gone to an extreme length, a Reaction naturally began to take place in men's minds. Such have been the alternations of opinion, from the earliest ages of human speculation. Man may perhaps have existed in an original condition in which he was only aware of the impressions of Sense; but his first attempts to analyse his perceptions brought under his notice Ideas as a separate element, essential to the existence of knowledge. Ideas were thenceforth almost the sole subject of the study of philosophers; of Plato and his disciples, professedly; of Aristotle, and still more of the followers and commentators of Aristotle, practically. And this continued till the time of Galileo, when the authority of the Senses again began to be asserted; for it was shown by the great discoveries which were then made, that the Senses had at least some share in the promotion of knowledge. As discoveries more numerous and more striking were supplied by Observation, the world gradually passed over to the opinion that the share which had been ascribed to Ideas in the formation of real knowledge was altogether a delusion, and that Sensation alone was true. But when this was asserted as a general doctrine, both its manifest falsity and its alarming consequences roused men's minds, and made them recoil from the extreme point to which they were approaching. Philosophy again oscillated back towards Ideas; and over a great part of Europe, in the clearest and most comprehensive minds, this regression from the dogmas of the Sensational School is at present the prevailing movement. We shall conclude our review by noticing a few indications of this state of things. FOOTNOTES: [Footnote 225: _Essay_, b. xi. c. iv. sect. 3.] [Footnote 226: _Ibid._ c. xiii. sect. 22.] [Footnote 227: _History of Ideas_, b. iii. c. iii. Modern Opinions respecting the Idea of Cause.] [Footnote 228: _Ibid._ b. i. c. iv.] [Footnote 229: _Langue des Calculs_, p. 1.] [Footnote 230: _Grammaire_, p. xxxvi.] [Footnote 231: Since the selection and construction of terms is thus a matter of so much consequence in the formation of science, it is proper that systematic rules, founded upon sound principles, should be laid down for the performance of this operation. Some such rules are accordingly suggested in b. iv. of the _Nov. Org. Ren._] [Footnote 232: _Disc. Prélim._ p. viii.] [Footnote 233: Helvetius _Sur l'Homme_, c. xxiii.] [Footnote 234: P. xiii.] CHAPTER XX. THE REACTION AGAINST THE SENSATIONAL SCHOOL.