Note 29 — ÉTUDE SUR STUART MILL

Here then is a complete application of the Method of Agreement, establishing the fact of an invariable connexion between the deposition of dew on a surface, and the coldness of that surface compared with the external air. But which of these is cause, and which effect? or are they both effects of something else? On this subject the Method of Agreement can afford us no light: we must call in a more potent method. We must collect more facts, or, which comes to the same thing, vary the circumstances; since every instance in which the circumstances differ is a fresh fact: and especially, we must note the contrary or negatives cases, i.e., where no dew is produced: for a comparison between instances of dew and instances of no dew is the condition necessary to bring the Method of Difference into play.