ABSTRACT
The scientific search for general truths is satisfied in some measure by the discovery of natural classes through the Method of Classification, and by ascertaining evolutionary sequences with the aid of the Evolutionary Method. In the former case, we discover certain uniformities of co-existence among the groups of essential characteristics of the several natural classes. The kinds of observations by which the man of science is led to surmise a real connection between certain facts, and the kinds of observation by which he then proceeds to test his surmise, or hypothesis, are often very similar. Their general character has been formulated in the five so-called Canons of Induction. The Method of Difference assumes various forms according to circumstances. Sometimes the several instances compared are really several successive states of the same set of circumstances, to which something is added to obtain the Positive Instance, or from which something is withdrawn to obtain the Negative Instance.
