One remark further: This constructive imagination at the third stage is the only one met with in many scientists. They lack genius for invention, but discover details, additions, corrections, improvements. A recent author distinguishes (a) those who have created the hypothesis, prepared the experiments, and imagined the appropriate apparatus; (b) those who have imagined the hypothesis and the experiment, but use means already invented; and (c) those who, having found the hypothesis made and demonstrated, have thought out a new method of verification.[116] The scientific imagination becomes poorer as we follow it down this scale, which, however, bears no relation to exactness of reasoning and firmness of method.
Neglecting species and varieties, we may reduce the fundamental characters of the scientific imagination to the following:
For its material, it has concepts, the degree of abstraction of which varies with the nature of the science.
It employs only those associational forms that have an objective basis, although its mission is to form new combinations, "the discoveries consisting of the relation of ideas, capable of being united, which hitherto have been isolated."[117] (Laplace.) All association with an affective basis is strictly excluded.
It aims toward objectivity: in its conjectural construction it attempts to reproduce the order and connection of things. Whence its natural affinity for realistic art, which is midway between fiction and reality.
It is unifying, and so just the opposite of the esthetic imagination, which is rather developmental. It puts forward the master idea (Claude Bernard's idée directrice), a center of attraction and impulse that enlivens the entire work. The principle of unity, without which no creation succeeds, is nowhere more visible than in the scientific imagination. Even when illusory, it is useful. Pasteur, scrupulous scientist that he was, did not hesitate to say: "The experimenter's illusions are a part of his power: they are the preconceived ideas serving as guides for him."
V
It does not seem to me wrong to regard the imagination of the metaphysician as a variety of the scientific imagination. Both arise from one and the same requirement. Several times before this we have emphasized this point—that the various forms of imagination are not the work of an alleged "creative instinct," but that each particular one has arisen from a special need. The scientific imagination has for its prime motive the need of partial knowledge or explanation; the metaphysical imagination has for its prime motive the need of a total or complete explanation. The latter is no longer an endeavor on a restricted group of phenomena, but a conjecture as to the totality of things, as aspiration toward completely unified knowledge, a need of final explanation that, for certain minds, is just as imperious as any other need.
This necessity is expressed by the creation of a cosmic or human hypothesis constructed after the type and methods of scientific hypotheses, but radically subjective in its origin—only apparently objective. It is a rationalized myth.
The three moments requisite for the constitution of a science are found here, but in a modified form: reflection replaces observation, the choice of the hypothesis becomes all-important, and its application to everything corresponds to scientific proof.