XX. True Sense of the Principle of Contradiction.--Kant's Opinion 126 XXI. Does the Principle of Contradiction merit the Title of Fundamental; and if so, in what Sense? 140 XXII. The Principle of Evidence 146 XXIII. The Criterion of Consciousness 151 XXIV. The Criterion of Evidence 157 XXV. The Objective Value of Ideas 163 XXVI. Can all Cognitions be reduced to the Perception of Identity? 171 XXVII. Continuation of the same subject 176 XXVIII. Continuation of the same subject 183 XXIX. Are there true Synthetic Judgments _a priori_ in the Sense of Kant? 188 XXX. Vico's Criterion 200 XXXI. Continuation of the same subject 212 XXXII. The Criterion on Common Sense 219 XXXIII. Error of Lamennais on Common Consent 230 XXXIV. Summary and Conclusion 253 BOOK SECOND. ON SENSATION. I. Sensation in Itself 249 II. Matter is incapable of Sensation 255 III. Sleep and Waking 263 IV. Relation of Sensations to an External World 267 V. An Idealist Hypothesis 273 VI. Is the External and Immediate Cause of Sensations a Free Cause? 276 VII. Analysis of the Objectiveness of Sensations 279 VIII. Sensation of Extension 283 IX. Objectiveness of the Sensation of Extension 287 X. Force of Touch to make Sensations Objective 293 XI. Inferiority of Touch compared with other Senses 296 XII. Can Sight alone give us the Idea of a Surface? 302 XIII. Cheselden's Blind Man 310 XIV. Can Sight give us the Idea of a Solid? 315 XV. Sight and Motion 319 XVI. Possibility of other Senses 324 XVII. Existence of New Senses 328 XVIII. Solution of Lamennais' Objection 333 BOOK THIRD. EXTENSION AND SPACE. I. Extension Inseparable from the Idea of Body 339