(2) Method of Agreement. Principle stated Method symbolized Method illustrated Distinguishing features of method A matter of observation and experiment Advantages and disadvantages (3) Method of Difference. Principle stated Method symbolized Method illustrated Advantages and disadvantages Characteristic features Agreement and Difference compared (4) The Joint Method of Agreement and Difference Principle stated Method symbolized Concrete illustrations Distinguishing features Advantages and disadvantages (5) Method of Concomitant Variations Principle stated Method symbolized Concrete illustrations Distinguishing features Advantages and disadvantages (6) The Method of Residues Principle stated Method symbolized Concrete illustrations Distinguishing features Advantages and disadvantages (7) General Purpose and Unity of Five Methods One fundamental principle =9. SUMMARY.= (1) The fundamental fact of causation underlies the three forms of induction, but is most conspicuous in the method of analysis and may be ascertained by recourse to one of the experimental methods. (2) The principle of the method of agreement may be summed up in the two statements: The sole invariable antecedent of a phenomenon is probably its cause and the sole invariable consequent of a phenomenon is probably its effect. These two statements may be symbolized and illustrated. The essential characteristics of the method of agreement are the phenomenon always occurs; there is at least one invariable antecedent; the other antecedents vary. The method of agreement together with the other four methods may justly be termed methods of experiment as well as methods of observation. The difficulties of the method of agreement are in the main plurality of causes, immaterial antecedents, complexity of phenomenon and uncertainty of conclusion. These difficulties may be summarized as involving a phenomenon which may have several causes; may be preceded by conditions of no causal consequence; may be so involved as to prevent exhaustive examination; and may give unreliable conclusions. Agreement is valuable chiefly in furnishing to the investigator plausible hypotheses. (3) The principle of difference is this: “Whatever is invariably present when the phenomenon occurs and invariably absent when the phenomenon does not occur, other circumstances remaining the same, is probably the cause or the effect of the phenomenon.” Like agreement, difference admits of symbolization and illustration by concrete examples. The chief difficulties attending difference are: in nature varying _one_ antecedent at a time is infrequent, and it is easy to overlook antecedents which are closely related to the case under investigation.