What science is. Science may be considered either as the product of a certain type of human activity, or as a human activity satisfactory even apart from its fruits. As an activity, it is a highly refined form of that process of reflection by which man is, in the first place, enabled to make himself at home in the world. It differs from the ordinary or common-sense process of thinking, as we shall presently see, in being more thoroughgoing, systematic, and sustained. It is common sense of a most extraordinarily refined and penetrating kind. But before examining the procedure of science, we must consider briefly its imposing product, that science whose vast structure seems to the layman so final, imposing, and irrefragable.
From the point of view of the product which is the fruit of reflective activity, Science may be defined as a body of systematized and verified knowledge, expressing in general terms the relations of exactly defined phenomena. In all the respects here noted, science may be contrasted with those matters of common knowledge, of opinion or belief which are the fruit of our casual daily thinking and experience. Science is, in the first place, a body of systematized knowledge. One has but to contrast the presentation of facts in an ordinary textbook in zoölogy with the random presentation of facts in a newspaper or in casual conversation. In science the facts bearing on a given problem are presented as completely as possible and are classified with reference to their significant bearings upon the problem. Moreover the facts gathered and the classifications of relationship made are not more or less accurate, more or less true; they are tested and verified results. That putrefaction, for example, is due to the life of micro-organisms in the rotting substance is not a mere assumption. It has been proved, tested, and verified by methods we shall have occasion presently to examine.
Scientific knowledge, moreover, is general knowledge. The relations it expresses are not true in some cases of the precise kind described, untrue in others. The relations hold true whenever these precise phenomena occur. This generality of scientific relations is closely connected with the fact that science expresses relations of exactly defined phenomena. When a scientific law expresses a certain relation between A and B, it says in effect: Given A as meaning this particular set of conditions and no others, and B as meaning this particular set of conditions and no others, then this relation holds true. The relations between exactly defined phenomena are expressed in general terms, that is, the relations expressed hold true, given certain conditions, whatever be the accompanying circumstances. It makes no difference what be the kind of objects, the law of gravitation still holds true: the attraction between objects is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.
Thus science as an activity is marked off by its method and its intent rather than by its subject-matter. As a method it is characterized by thoroughness, persistency, completeness, generality, and system. As regards its intent, it is characterized by its freedom from partiality or prejudice, and its interest in discovering what the facts are, apart from personal expectations and desires. In the scientific mood we wish to know what the nature of things is. There are men who seem to have a boundless, insatiable curiosity, who have a lifelong passion for acquiring facts and understanding the relationship between them.
Science as explanation. The satisfactions which scientific investigators derive from their inquiries are various. There is, in the first place, the sheer pleasure of gratifying the normal human impulse of curiosity, developed in some people to an extraordinary degree. Experience to a sensitive and inquiring mind is full of challenges and provocations to look further. The appearance of dew, an eclipse of the sun, a flash of lightning, a peal of thunder, even such commonplace phenomena as the falling of objects, or the rusting of iron, the evaporation of water, the melting of snow, may provoke inquiry, may suggest the question, "Why?" Experience, as it comes to us through the senses, is broken and fragmentary. The connections between the occurrences of Nature seem casual, and connected, as it were, purely by accident. A black sky portends rain. But such an inference made by the untrained mind is merely the result of habit. A black sky has been followed by rain in the past; the same sequence of events may be expected in the future. But the connection between the two is not really understood. Sometimes experiences seem to contradict each other. The straight stick looks crooked or broken in water. The apparent anomalies and contradictions, the welter of miscellaneous facts with which we come in contact through the experiences of the senses, are clarified by the generalizations of science. The world of facts ceases to be random, miscellaneous, and incalculable. Every phenomenon that occurs is seen to be an instance of a general law that holds among all phenomena that resemble it in certain definable respects. Thus the apparent bending of the stick in water is seen to be a special case of the laws of the refraction of light; the apparent anomaly or contradiction of our sense experiences is, as we say, explained. What seemed to be a contradiction and an exception is seen to be a clear case of a regular law.
The desire for explanation in some minds is very strong. Science explains in the sense that it reduces a phenomenon to the terms of a general principle, whatever that principle may be. When we meet a phenomenon that seems to come under no general law, we are confronted with a mystery and a miracle. We do not know what to expect from it. But when we can place a phenomenon under a general law, applicable in a wide variety of instances, everything that can be said of all the other instances in which the law applies, applies also to this particular case.
Think of heat as motion, and whatever is true of motion will be true of heat; but we have had a hundred experiences of motion for everyone of heat. Think of the rays passing through this lens as bending toward the perpendicular, and you substitute for the comparatively unfamiliar lens the very familiar notion of a particular change in direction of a line, of which motion every day brings us countless examples.[1]
[Footnote 1: James: Psychology, vol. II, p. 342.]
It must be noticed that the explanation which science gives, is really in answer to the question, "How?" not the question, "Why?" We are said to understand phenomena when we understand the laws which govern them. But to say that certain given phenomena—the appearance of dew, the falling of rain, the flash of lightning, the putrefaction of animal matter—obey certain laws is purely metaphorical. Phenomena do not obey laws in the sense in which we say the child follows the commands of his parents, or the soldier those of his officer. The laws of science simply describe the relations which have repeatedly been observed to exist between phenomena. They are laws in the sense that they are invariably observed successions. When it has been found that whenever A is present, B is also present, that the presence of A is always correlated with the presence of B, and the presence of B is always correlated with the presence of A, we say we have discovered a scientific law.
Science thus explains in the sense that it reduces the multiplicity and variety of phenomena to simple and general laws. The ideal of unity and simplicity is the constant ideal toward which science moves, and its success in thus reducing the miscellaneous facts of experience has been phenomenal. The history of science in the nineteenth century offers some interesting examples. The discovery of the conservation of energy and its transformations has revealed to us the unity of force. It has shown, for example, that the phenomenon of heat could be explained by molecular motions. "Electricity annexed magnetism." Finally the relations of electricity and light are now known; "the three realms of light, of electricity and of magnetism, previously separated, form now but one; and this annexation seems final."