In every inquiry in which there are principles or causes or elements, understanding and science occur from knowing these. For we think we know each thing when we know the first causes and first principles and have reached the elements. It is clear, then, that in natural science as well one must try to determine first what concerns the principles.
The natural path is to go from things which are more known and certain to us toward things which are more certain and more knowable by nature. For the more known to us and the simply knowable are not the same. … For the whole is more known according to sensation, and the universal is a certain whole. For the universal embraces many things within it as parts. ~ Physics, I.1
And George Eliot provides us with a dramatic example:
Perhaps that was a more cheerful time for observers and theorizers than the present; we are apt to think it the finest era of the world when America was beginning to be discovered, when a bold sailor, even if he were wrecked, might alight on a new kingdom; and about 1829 the dark territories of Pathology were a fine America for a spirited young adventurer. Lydgate was ambitious above all to contribute towards enlarging the scientific, rational basis of his profession. The more he became interested in special questions of disease, such as the nature of fever or fevers, the more keenly he felt the need for that fundamental knowledge of structure which just at the beginning of the century had been illuminated by the brief and glorious career of Bichat, who died when he was only one-and-thirty, but, like another Alexander, left a realm large enough for many heirs. That great Frenchman first carried out the conception that living bodies, fundamentally considered, are not associations of organs which can be understood by studying them first apart, and then as it were federally; but must be regarded as consisting of certain primary webs or tissues, out of which the various organs—brain, heart, lungs, and so on—are compacted, as the various accommodations of a house are built up in various proportions of wood, iron, stone, brick, zinc, and the rest, each material having its peculiar composition and proportions. No man, one sees, can understand and estimate the entire structure or its parts—what are its frailties and what its repairs, without knowing the nature of the materials. And the conception wrought out by Bichat, with his detailed study of the different tissues, acted necessarily on medical questions as the turning of gas-light would act on a dim, oil-lit street, showing new connections and hitherto hidden facts of structure which must be taken into account in considering the symptoms of maladies and the action of medicaments. But results which depend on human conscience and intelligence work slowly, and now at the end of 1829, most medical practice was still strutting or shambling along the old paths, and there was still scientific work to be done which might have seemed to be a direct sequence of Bichat’s. This great seer did not go beyond the consideration of the tissues as ultimate facts in the living organism, marking the limit of anatomical analysis; but it was open to another mind to say, have not these structures some common basis from which they have all started, as your sarsnet, gauze, net, satin, and velvet from the raw cocoon? Here would be another light, as of oxy-hydrogen, showing the very grain of things, and revising all former explanations. Of this sequence to Bichat’s work, already vibrating along many currents of the European mind, Lydgate was enamoured; he longed to demonstrate the more intimate relations of living structure, and help to define men’s thought more accurately after the true order. The work had not yet been done, but only prepared for those who knew how to use the preparation. What was the primitive tissue? In that way Lydgate put the question—not quite in the way required by the awaiting answer; but such missing of the right word befalls many seekers. And he counted on quiet intervals to be watchfully seized, for taking up the threads of investigation—on many hints to be won from diligent application, not only of the scalpel, but of the microscope, which research had begun to use again with new enthusiasm of reliance. Such was Lydgate’s plan of his future: to do good small work for Middlemarch, and great work for the world. ~ Middlemarch, Bk. 2, ch. 15