can do it. Now I hold that this second step in the process can only be taken very rarely, no matter how certain we assume ourselves to be of the uniformity of nature. I hold that the canons of his various experimental methods formulate the process of induction as it would have to be if it terminated in what would justify belief to a pure intellect, but that they utterly fail to describe the process of induction which we are familiar with in our experience. "If two or more instances of the phenomenon under investigation," says the canon of the Method of Agreement, "have only one circumstance in common, the circumstance in which alone all the instances agree, is the cause (or effect) of the given phenomenon."[1] Upon this canon the obvious criticism is, that it presupposes a condition that is never realized. If two or more instances of the phenomenon under investigation had only one circumstance in common and we could be sure of it, all would be plain sailing, but any such instance has an indefinite number of circumstances in common with every other. To this, of course, a follower of Mill would reply that although they do, they have only a limited number of circumstances in common that can be supposed to be material to the result. That was Mill's own answer. "The extent and minuteness of observation," he said, "which may be requisite . . . depends on the particular purpose in view. To ascertain the state of the whole universe at any moment is impossible, but would also be useless. In making chemical experiments, we do not think it necessary to note the position of the planets ; because experience has shown, as a very superficial experience is sufficient to show, that in such cases that circumstance is not material to the result;[2] and, accordingly, in the ages when men believed in the occult influences of the heavenly bodies, it might have been unphilosophical to omit ascertaining the precise condition of those bodies at the moment of the experiment."[3] But if one asks for the method by which experience shows what circumstances are possibly material to the result and what not, the answer must be induc-
