§1. The Canon of Agreement 206 Negative Instances (p. 208); Plurality of Causes (p. 208) Agreement may show connection without direct Causation (p. 209) §2. The Canon of Agreement in Presence and in Absence 212 It tends to disprove a Plurality of Causes (p. 213) §3. The Canon of Difference 216 May be applied to observations (p. 221) §4. The Canon of Variations 222 How related to Agreement and Difference (p. 222); The Graphic Method (p. 227); Critical points (p. 230); Progressive effects (p. 231); Gradations (p. 231) §5. The Canon of Residues 232 CHAPTER XVII COMBINATION OF INDUCTION WITH DEDUCTION §1. Deductive character of Formal Induction 236 §2. Further complication of Deduction with Induction 238 §3. The Direct Deductive (or Physical) Method 240 §4. Opportunities of Error in the Physical Method 243 §5. The Inverse Deductive (or Historical) Method 246 §6. Precautions in using the Historical Method 251 §7. The Comparative Method 255 §8. Historical Evidence 261 CHAPTER XVIII HYPOTHESES §1. Hypothesis defined and distinguished from Theory 266 §2. An Hypothesis must be verifiable 268 §3. Proof of Hypotheses 270 (1) Must an hypothetical agent be directly observable? (p. 270); _Vera causa_ (p. 271) (2) An Hypothesis must be adequate to its pretensions (p. 272); _Exceptio probat regulam_ (p. 274) (3) Every competing Hypothesis must be excluded (p. 275); Crucial instance (p. 277) (4) Hypotheses must agree with the laws of Nature (p. 279) §4. Hypotheses necessary in scientific investigation 280 §5. The Method of Abstractions 283 Method of Limits (p. 284); In what sense all knowledge is hypothetical (p. 286) CHAPTER XIX LAWS CLASSIFIED; EXPLANATION; CO-EXISTENCE; ANALOGY