The order of our ideas, 253. It is determined by cerebral laws, 255. The ultimate cause of association is habit, 256. The elementary law in association, 257. Indeterminateness of its results, 258. Total recall, 259. Partial recall, and the law of interest, 261. Frequency, recency, vividness, and emotional congruity tend to determine the object recalled, 264. Focalized recall, or 'association by similarity,' 267. Voluntary trains of thought, 271. The solution of problems, 273. Similarity no elementary law; summary and conclusion, 277. CHAPTER XVII. THE SENSE OF TIME 280 The sensible present has duration, 280. We have no sense for absolutely empty time, 281. We measure duration by the events which succeed in it, 283. The feeling of past time is a present feeling, 285. Due to a constant cerebral condition, 286. CHAPTER XVIII. MEMORY 287 What it is, 287. It involves both retention and recall, 289. Both elements explained by paths formed by habit in the brain, 290. Two conditions of a good memory, persistence and numerousness of paths, 292. Cramming, 295. One's native retentiveness is unchangeable, 296. Improvement of the memory, 298. Recognition, 299. Forgetting, 300. Pathological conditions, 301. CHAPTER XIX. IMAGINATION 302 What it is, 302. Imaginations differ from man to man; Galton's statistics of visual imagery, 303. Images of sounds, 306. Images of movement, 307. Images of touch, 308. Loss of images in aphasia, 309. The neural process in imagination, 310. CHAPTER XX. PERCEPTION 312 Perception and sensation compared, 312. The perceptive state of mind is not a compound, 313. Perception is of definite things, 316. Illusions, 317. First type: inference of the more usual object, 318. Second type: inference of the object of which our mind is full, 321. 'Apperception,' 326. Genius and old-fogyism, 327. The physiological process in perception, 329. Hallucinations, 330. CHAPTER XXI. THE PERCEPTION OF SPACE 335 The attribute of extensity belongs to all objects of sensation, 335. The construction of real space, 337. The processes which it involves: 1) Subdivision, 338; 2) Coalescence of different sensible data into one 'thing,' 339; 3) Location in an environment, 340; 4) Place in a series of positions, 341; 5) Measurement, 342. Objects which are signs, and objects which are realities, 345. The 'third dimension,' Berkeley's theory of distance, 346. The part played by the intellect in space-perception, 349. CHAPTER XXII. REASONING 351