It has often been said that the perfection of a science is measured by the amount of mathematics it requires; we might say, conversely, that its lack of completeness is measured by the amount of imagination that it includes. It is a psychological necessity. Where the human mind cannot explain or prove, there it invents; preferring a semblance of knowledge to its total absence.[110] Imagination fulfills the function of a substitute; it furnishes a subjective, conjectural solution in place of an objective, rational explanation. This substitution has degrees:
(1) The sway of the imagination is almost complete in the pseudo-sciences (alchemy, astrology, magic, occultism, etc.), which it would be more proper to call embryonic sciences, for they were the beginnings of more exact disciplines and their fancies have not been without use. In the history of science, this is the golden age of the creative imagination, corresponding to the myth-making period already studied.
(2) The semi-sciences, incompletely proved (certain portions of biology, psychology, sociology, etc.), although they show a regression of imaginative explanation repulsed by the hitherto absent or insufficient experimentation, nevertheless abound in hypotheses, that succeed, contradict, destroy one another. It is a commonplace truism that does not need to be dwelt on—they furnish ad libitum examples of what has been rightly termed scientific mythology.
Aside from the quantity of imagination expended, often without great profit, there is another character to be noted—the nature of the belief that accompanies imaginative creation. We have already seen repeatedly that the intensity of the imaginary conception is in direct ratio to the accompanying belief, or rather, that the two phenomena are really one—merely the two aspects of one and the same state of consciousness. But faith—i.e., the adherence of the mind to an undemonstrated assertion—is here at its maximum.
There are in the sciences hypotheses that are not believed in, that are preserved for their didactic usefulness, because they furnish a simple and convenient method of explanation. Thus the "properties of matter" (heat, electricity, magnetism, etc.), regarded by physicists as distinct qualities even in the first half of the last century; the "two electric fluids;" cohesion, affinity, etc., in chemistry—these are some of the convenient and admitted expressions to which, however, we attach no explanatory value.
There is also to be mentioned the hypothesis held as an approximation of reality—this is the truly scientific position. It is accompanied by a provisional and ever-revocable belief. This is admitted, in principle at least, by all scientists, and has been put into practice by many of them.
Lastly, there is the hypothesis regarded as the truth itself—one that is accompanied by a complete, absolute, belief. But daily observation and history show us that in the realm of embryonic and ill-proven sciences this disposition is more flourishing than anywhere else. The less proof there is, the more we believe. This attitude, however wrong from the standpoint of the logician, seems to the psychologist natural. The mind clings tenaciously to the hypothesis because the latter is its own creation, or, because in adopting it, it seems to the mind that it should have itself discovered the hypothesis, so much does the latter harmonize with its inner states. Let us take the hypothesis of evolution, for example: we need not mention its high philosophical bearing, and the immense influence that it exerts on almost all forms of human thought. Nevertheless, it still remains an hypothesis; but for many it is an indisputable and inviolable dogma, raised far above all controversy. They accept it with the uncompromising fervor of believers: a new proof of the underlying connection between imagination and belief—they increase and decrease pari passu.
III
Should we assign as belonging solely to the imagination every invention or discovery—in a word, whatever is new—in the well-organized sciences that form a body of solid, constantly-broadening doctrine? It is a hard question. That which raises scientific knowledge above popular knowledge is the use of an experimental method and rigorous reasoning processes; but, is not induction and deduction going from the known to the unknown? Without desiring to depreciate the method and its value, it must nevertheless be admitted that it is preventive, not inventive. It resembles, says Condillac, the parapets of a bridge, which do not help the traveler to walk, but keep him from falling over. It is of value especially as a habit of mind. People have wisely discoursed on the "methods" of invention. There are none; but for which fact we could manufacture inventors just as we make mechanics and watchmakers. It is the imagination that invents, that provides the rational faculties with their materials, with the position, and even the solution of their problems. Reasoning is only a means for control and proof; it transforms the work of the imagination into acceptable, logical results. If one has not imagined beforehand, the logical method is aimless and useless, for we cannot reason concerning the completely unknown. Even when a problem seems to advance towards solution wholly through the reason, the imagination ceaselessly intervenes in the form of a succession of groupings, trials, guesses, and possibilities that it proposes. The function of method is to determine its value, to accept or reject it.[111]
Let us show by a few examples that conjecture, the work of the combining imagination, is at the root of the most diverse scientific inventions.[112]