§1. Axioms; Primary Laws; Secondary Laws, Derivative or Empirical; Facts 288 §2. Secondary Laws either Invariable or Approximate Generalisations 292 §3. Secondary Laws trustworthy only in 'Adjacent Cases' 293 §4. Secondary Laws of Succession or of Co-existence 295 Natural Kinds (p. 296); Co-existence of concrete things to be deduced from Causation (p. 297) §5. Explanation consists in tracing resemblance, especially of Causation 299 §6. Three modes of Explanation 302 Analysis (p. 302); Concatenation (p. 302); Subsumption (p. 303) §7. Limits of Explanation 305 §8. Analogy 307 CHAPTER XX PROBABILITY §1. Meaning of Chance and Probability 310 §2. Probability as a fraction or proportion 312 §3. Probability depends upon experience and statistics 313 §4. It is a kind of Induction, and pre-supposes Causation 315 §5. Of Averages and the Law of Error 318 §6. Interpretation of probabilities 324 Personal Equation (p. 325); meaning of 'Expectation' (p. 325) §7. Rules of the combination of Probabilities 325 Detection of a hidden Cause (p. 326); oral tradition (p. 327); circumstantial and analogical evidence (p. 328) CHAPTER XXI DIVISION AND CLASSIFICATION §1. Classification, scientific, special and popular 330 §2. Uses of classification 332 §3. Classification, Deductive and Inductive 334 §4. Division, or Deductive Classification: its Rules 335 §5. Rules for testing a Division 337 §6. Inductive Classification 339 §7. Difficulty of Natural Classification 341 §8. Darwin's influence on the theory of Classification 342 §9. Classification of Inorganic Bodies also dependent on Causation 346 CHAPTER XXII NOMENCLATURE, DEFINITION, PREDICABLES