1. THE AIM OF THE FIVE METHODS.
The primary forms of induction have been divided into simple enumeration, analogy and analysis. Conditioning these forms are the two laws, uniformity of nature and universal causation. Since these laws are always concerned with causes, we may refer to them as together expressing the fundamental “fact of causation.” Wherever there is a causal connection, no matter how slight, these laws obtain.
Though “the fact of causation” probably conditions all forms of induction, it is most conspicuous in the third form; namely, Analysis. Here the main aim is to establish a causal connection of some kind; an aim which may be accomplished through the medium of observation and experiment. Incident to this notion, John Stewart Mill formulated five experimental methods of induction. These are known according to the following distinctive titles:
1. The Method of Agreement.
2. The Method of Difference.
3. The Joint Method of Agreement and Difference.
4. The Method of Concomitant Variations.
5. The Method of Residues.
2. METHOD OF AGREEMENT.
(1) Principle stated. As stated by Mill the principle of the Method of Agreement is this: “If two or more instances of the phenomenon under investigation have only one circumstance in common, the circumstances in which alone all the instances agree is the cause (or effect) of the given phenomenon.”