“When we compare the infinite multitude of the phenomena of nature with the limits of our understandings and the weakness of our organs, can we ever expect anything else from the slowness of our work, from the long and frequent interruptions, and from the rarity of creative genius than a few broken and separated pieces of the great chain that binds all things together? Experimental philosophy might work for centuries of centuries, and the materials that it had heaped up, finally reaching in their number beyond all combination, would still be far removed from an exact enumeration. How many volumes would it not need to contain the mere terms by which we should designate the distinct collections of phenomena, if the phenomena were known? When will the philosophic language be complete? If it were complete, who among men would be able to know it? If the Eternal, to manifest his power still more plainly than by the marvels of nature, had deigned to develop the universal mechanism on pages traced by his own hand, do you suppose that this great book would be more comprehensible to us than the universe itself? How many pages of it all would have been intelligible to the philosopher who, with all the force of head that had been conferred upon him, was not sure of having grasped all the conclusions by which an old geometer determined the relation of the sphere to the cylinder? We should have in such pages a fairly good measure of the reach of men’s minds, and a still more pungent satire on our vanity. We should say, Fermat went to such a page, Archimedes went a few pages further.
“What then is our end? The execution of a work that can never be achieved, and which would be far beyond human intelligence if it were achieved. Are we not more insensate than the first inhabitants of the plain of Shinar? We know the immeasurable distance between the earth and the heavens, and still we insist on rearing our tower.
“But can we presume that there will not come a time when our pride will abandon the work in discouragement? What appearance is there that, narrowly lodged and ill at its ease here below, our pride should obstinately persist in constructing an uninhabitable palace beyond the earth’s atmosphere? Even if it should so insist, would it not be arrested by the confusion of tongues, which is already only too perceptible and too inconvenient in natural history? Besides, it is utility that circumscribes all. It will be utility that in a few centuries will set bounds to experimental physics, as it is on the eve of setting bounds to geometry. I grant centuries to this study, because the sphere of its utility is infinitely more extensive than that of any abstract science, and it is without contradiction the base of our real knowledge.”[212]
We cannot wonder that when Comte drew up his list of the hundred and fifty volumes that should form the good Positivist’s library in the nineteenth century, he should have placed Diderot’s Interpretation of Nature on one side of Descartes’ Discourse on Method, with Bacon’s Novum Organum on the other.
The same spirit finds even stronger and more distinct expression in a later aphorism:—“Since the reason cannot understand everything, imagination foresee everything, sense observe everything, nor memory retain everything; since great men are born at such remote intervals, and the progress of science is so interrupted by revolution, that whole ages of study are passed in recovering the knowledge of the centuries that are gone,—to observe everything in nature without distinction is to fail in duty to the human race. Men who are beyond the common run in their talents ought to respect themselves and posterity in the employment of their time. What would posterity think of us if we had nothing to transmit to it save a complete insectology, an immense history of microscopic animals? No—to the great geniuses great objects, little objects to the little geniuses” (§ 54).
Diderot, while thus warning inquirers against danger on one side, was alive to the advantages of stubborn and unlimited experiment on the other. “When you have formed in your mind,” he says, “one of those systems which require to be verified by experience, you ought neither to cling to it obstinately nor abandon it lightly. People sometimes think their conjectures false, when they have not taken the proper measures to find them true. Obstinacy, even, has fewer drawbacks than the opposite excess. By multiplying experiments, if you do not find what you want, it may happen that you will come on something better. Never is time employed in interrogating nature entirely lost” (§ 42). The reader will not fail to observe that this maxim is limited by the condition of verifiableness. Of any system that could not be verified by experience Diderot would have disdained to speak in connection with the interpretation of nature.
This, of course, did not prevent him from hypothesis and prophecy which he himself had not the means of justifying. For example, he said that just as in mathematics, by examining all properties of a curve we find that they are one and the same property presented under different faces, so in nature when experimental physics are more advanced, people will recognise that all the phenomena, whether of weight, or elasticity, or magnetism, or electricity, are only different sides of the same affection (§ 44). But he was content to leave it to posterity, and to build no fabric on unproved propositions.
In the same scientific spirit he penetrated the hollowness of every system dealing with Final Causes:
“The physicist, whose profession is to instruct and not to edify, will abandon the Why, and will busy himself only with the How.... How many absurd ideas, false suppositions, chimerical notions in those hymns which some rash defenders of final causes have dared to compose in honour of the Creator? Instead of sharing the transports of admiration of the prophet, and crying out at the sight of the unnumbered stars that light up the midnight sky, The heavens declare the glory of God, and the firmament sheweth his handiwork, they have given themselves up to the superstition of their conjectures. Instead of adoring the All-Powerful in the creation of nature, they have prostrated themselves before the phantoms of their imagination. If any one doubts the justice of my reproach, I invite him to compare Galen’s treatise on the use of parts of the human body, with the physiology of Boerhaave, and the physiology of Boerhaave with that of Haller; I invite posterity to compare the systematic or passing views of Haller with what will be the physiology of future times. Man praises the Eternal for his own poor views; and the Eternal who hears from the elevation of his throne, and who knows his own design, accepts the silly praise and smiles at man’s vanity” (§ 56).
The world has advanced rapidly along this path since Diderot’s day, and has opened out many new and unsuspected meanings by the way. Perhaps the advance has been less satisfactory in working out, in a scientific way, the philosophy that is implied in the following adaptation of the Leibnitzian and Maupertuisian suggestion of the law of economy in natural forces:—“Astonishment often comes from our supposing several marvels, where in truth there is only one; from our imagining in nature as many particular acts as we can count phenomena, whilst nature has perhaps in reality never produced more than one single act. It seem even that, if nature had been under the necessity of producing several acts, the different results of such acts would be isolated; that there would be collections of phenomena independent of one another, and that the general chain of which philosophy assumes the continuity, would break in many places. The absolute independence of a single fact is incompatible with the idea of an All; and without the idea of a Whole, there can be no Philosophy” (§ 11).