§49. Experiments among the Monads
Leibniz is a friend of experience because he is a friend to humanity. Most of what we require “for the effective conduct of life” we have “derived from experience.” From signs, as Hobbes said; medical signs, natural, empirical indications.
But (as Hobbes also concluded) that is not science. “The utility of experiments is of two kinds: one for the varied conveniences of life, which are revealed by reasoning from cause to effect; the other to bring to light true principles, by proceeding from effects to causes.” Referring to principles advanced from geometry and mechanics, he says, “Reason must supply this most important lack in experiment.” Experience satisfies animal need, but—and here the difference from Hobbes—a duly qualified experiment contributes to science. Experiment is experience conceptualized, rationalized, disciplined by an art of reasoning. “The most outstanding experiments are in vain if men who will use them are lacking.” The method of reasoning from experiments to causes “needs to be cultivated more widely and with greater care than heretofore.”193It is his constant theme. Experiments are good, but we do not use them well. Writing in 1671, he self-identifies as an experimental philosopher (philosophis experimentalibus). Forty-five years later (1715) he still declares himself “strongly in favor of experimental philosophy.” Writing to Huygens, he said, “I prefer a Leeuwenhoek who tells me what he sees than a Cartesian who tells me what he thinks.” There is, then, no question as to the value of experiments (including observation). The question is by what rule should their evidence be taken into scientific reasoning. Leibniz goes back to Hippocrates, to the medical method Plato described. “The true method of reasoning from experiments is this—we must resolve every phenomenon into all its circumstances by considering separately color, odor, taste, heat, and cold, and other tactile qualities, and finally the common attributes of magnitude, figure, and motion.
Now if we have discovered the cause of each of these attributes in itself we will certainly have the cause of the whole phenomenon.”194The preference for Leeuwenhoek over Descartes means that many natural philosophical questions are better handled by the observation of nature than by close ratiocination. Leibniz is more of an empiricist than we typically recognize. He was an alchemist, and served a term as secretary to an alchemical society in Nuremberg. He admires Galen as an observer and experimentalist. He followed animal experiments closely and was a staunch advocate of vivisection. He wrote treatises on public health and medical questions, and declared medicine “the most necessary of the natural sciences... the summit and as it were the principal fruit of our knowledge of bodies.” Thinking of medicine gives him fresh reason for exasperation with Descartes. “It is true that M. Descartes applied himself to medicine from time to time, but one would wish that he had applied himself more, and with more attention to observations than to hypotheses.” “May it please God that it should come about that doctors philosophize and philosophers occupy themselves with medicine.”195
Leibniz’s principal discussion of experience and experiments is in the New Essays on Human Understanding, his examination of Locke’s Essay. He takes the view that observation and experiment are indispensable to natural philosophy, but they cannot play the leading role that Boyle assigns them. They are brought into natural philosophy to compensate for our finitude. God does not need experience for knowledge. However, experience is not the creative force in natural philosophy. Everything creative is in the concepts. Experience helps decide which logically possible mechanism actually operates in nature, but it cannot create a concept. “In medicine... there could not be too many observations—those first principles of experience—giving reason more chance to decipher things which nature has only half-revealed to us.” Experience provides data and tests, reason creates the science.196
Leibniz visited London in 1673, and meet several times with Boyle.
He admired Boyle's experimental procedures and sought clues to their logic and limitations. He approves Boyle's philosophical definition of “nature” as “the very mechanism of bodies itself,” and was impressed by the experimental demonstration of “intestine motions” in bodies apparently at rest, invisible to sense but responsible for macroscopic qualities. Boyle has advanced beyond Bacon and discovered causes that would otherwise remain in darkness, hence the challenge Leibniz faced of incorporating experimentation into his concept of science.197He concedes something to Locke's appeal to experience and also to Bacon and Boyle on experiments. Their mistake is one-sidedness. Leibniz may have instigated the canard about Bacon denying the value of a creative hypothesis. He praises Bacon for reducing the art of experiments to a rule, and praises Boyle for his practice of it, but we need more. We lack the “art of using experiments and of drawing conclusions from them.” Boyle, for example, wastes time trying to prove superfluous things. “Mr Boyle spend[s] rather too long on drawing from countless fine experiments no conclusion except one which he could have adopted as a principle, namely that everything in nature takes place mechanically—a principle which can be made certain by reason alone, and never by experiments, howsoever many of them one conducts.”198
Nothing in science is created by observation, but observations and experiments are helpful, even necessary for verifying conceptual structures, identifying which of the logical possibilities God actualized, and this verification is required, contrary to Hobbes and Epicurus. Leibniz stands with Galileo. “The senses provide the occasion, and successful experiments also serve to corroborate reason, somewhat as checks in arithmetic help us to avoid errors of calculation in long chains of reasoning.”199