not produced. And thus have been realized the requisitions of what we have termed the Indirect Method of Difference, or the Joint Method of Agreement and Difference."1

Here several things are confused. The pure method of difference was employed in showing that bodies with dew differed from those without dew simply in being colder than the air. An exhaustive examination established the general negative that dew occurs nowhere else; but this proves, not that coldness is the cause of dew, but that there is no other cause. Suppose that the question had been of heating caused by friction. Two cases agreeing only in the circumstance friction, and in the event heating, would meet the requirements of the first part of the canon; but we cannot prove the universal negative that heating never occurs without friction, and it is inconceivable that any confirmation. could be found in the properties of lenses, or the fall of Constantinople.

Dr. Fowler added to Mr. Mill's canon the words: "Moreover (supposing the requirements of the Method to be rigorously fulfilled), the circumstance proved by the method to be the cause is the only cause of the phenomenon." He does not tell us how the requirement of finding "two or more instances from which the phenomenon is absent" can be rigorously fulfilled, but a little reflection will show that it is by proving a universal negative; this, certainly, is rigor in finding "two or more" negative instances.

4. The Method of Concomitant Variations, which corresponds to our Cases 3 and 4 under Canon 1, is used upon some very interesting facts, but logically Logic, p. 299.

1

has no distinctness from the ordinary method of difference. Nor does the language need to be so elastic. The cases in which the consequent seems to decrease when the antecedent increases are only verbally different from those in which both increase together. All can be stated in terms of increase. For instance, instead of saying "the more heat the less condensation," we may say "the more expansion." Each pair of instances of concomitant variation affords a complete opportunity for the regular application of the test of difference, and the other pairs of cases, which are innumerable, simply enable us to proceed at once to a primary induction.

5. Mr. Mill seems to have exaggerated, with paternal partiality, the importance of these methods, which he had formulated and named and presented to the philosophical world. He says:

"The four methods which it has now been attempted to describe, are the only possible modes of experimental inquiry — of direct induction a posteriori, as distinguished from deduction; at least I know not, nor am able to imagine any others. And even of these, the Method of Residues, as we have seen, is not independent of deduction; though, as it also requires specific experience, it may, without impropriety, be included among methods of direct observation and experiment. These then, with such assistance as can be obtained from deduction, compose the available resources of the human mind for ascertaining the laws of the succession of phenomena." 1

According to this, the whole of Induction is concerned with facts of causation; no place is reserved for facts of coexistence or of likeness, or for the inductions built upon them. Nor, indeed, is any explicit provision

1 Logic, p. 291.

made for constructing inductions of any kind out of facts. But the facts isolated by these tests must be treated by the mind just like any other data of observation. They are not inductions, but must be generalized into primary inductions, or syllogized into secondary or mixed inductions, if they are to teach us anything. The test of difference gives immediate certainty, each time, regarding one solitary fact of causation. The test of agreement gives, upon the comparison of the first two instances, only a slight presumption of one fact of causation, but this slight probability, upon the comparison of more instances, gradually strengthens into a primary induction of a causal connection in all the instances. It should not be forgotten that no general truth can ever be reached in inductive logic except by a primary induction, directly used, or applied as one of the premises of a syllogism. Mr. Mill seems to think that all of the inductive thought of antiquity was simple enumeration, and that the use of the methods is the characteristic of modern science. He speaks of the ancients with their inductio per enumerationem simplicem," somewhat contemptuously. But, of course, the ancients isolated facts, by the methods of agreement and of difference, every hour of their lives; for they could not make primary inductions without isolating facts. The thinking of the ancients was inexact, but they were not unaccustomed to any fundamental operation of the mind. The characteristic difference between their thinking and ours cannot be, that we have substituted precision in isolating facts, for rashness in generalizing; the two things are not in the same plane. It is impossible to avoid the belief that what

led Mr. Mill to regard the methods as so much more scientific than inductio per enumerationem simplicem was the deductive process, involved in making a secondary induction, which he immediately performed after isolating a single fact of causation, and by which he reached at once a trustworthy generalization.

CHAPTER XIII.

HYPOTHESIS.

WHENEVER We meet with a disconnected fact, the mind instinctively seeks to refer it to some place in the general order. An Hypothesis is a conjecture made to account for some unexplained fact or facts. To account for a fact is to refer it to some uniformity or conjunction of uniformities. To speak then more exactly, an Hypothesis is the reference of a fact to a uniformity or a conjunction of uniformities, before we have evidence enough to feel sure about it. The word Theory is often used as synonymous with hypothesis; but it would be better to call the reference an hypothesis before we feel sure of its truth, and a theory after we become sure.

There is no other way to account for facts, except to refer them to uniformities. For the uniformities themselves, no reason can be given. The mind is satisfied with them as finalities. If one asks, Why is that bird black? and is answered, That is a crow and all crows are black, he accepts that answer as sufficient. Or if, being a chemist, he is led to ask, What pigment makes the crow's feathers black? when he finds the presence of a certain substance which is always black, he is satisfied. Newton asks why that apple falls, and having generalized that all things fall towards each other, is glorified as having explained the fall of the apple.