Historical Science, Experimental Science, and the Scientific Method

Historical science, experimental science, and the scientific method Carol E. Cleland Department of Philosophy and Center for Astrobiology, University of Colorado, Boulder, Colorado 80309, USA ABSTRACT Many scientists believe that there is a uniform, interdisciplinary method for the practice of good science. The paradigmatic examples, however, are drawn from classical experimental science. Insofar as historical hypotheses cannot be tested in controlled laboratory settings, historical research is sometimes said to be inferior to experimental research. Using examples from diverse historical disciplines, this paper demonstrates that such claims are misguided. First, the reputed superiority of experimental research is based upon accounts of scientific methodology (Baconian inductivism or falsificationism) that are deeply flawed, both logically and as accounts of the actual practices of scientists. Second, although there are fundamental differences in methodology between experimental scientists and historical scientists, they are keyed to a pervasive feature of nature, a time asymmetry of causation. As a consequence, the claim that historical science is methodo- logically inferior to experimental science cannot be sustained. Keywords: methodology, induction, history, experimental investigations. INTRODUCTION This paper explains why historical science is not inferior to ex- Experimental methods are commonly held up as the paradigm for perimental science when it comes to testing hypotheses. First, objec- testing hypotheses: the scientific method, widely disseminated in intro- tions such as Gee’s are based upon common misconceptions about ductory science texts, is modeled upon them. But not all scientific experimental practice and scientific methodology in general. Second, hypotheses can be tested in the laboratory. Historical hypotheses that the differences in methodology that actually do exist between historical postulate particular past causes for currently observable phenomena and experimental science are founded upon a remarkably pervasive provide good examples. Although historical hypotheses are usually as- feature of nature: a causal asymmetry between present and past events, sociated with fields such as paleontology and archaeology, they are on the one hand, and present and future events, on the other. Insofar also common in geology, planetary science, astronomy, and astro- as each practice is tailored to exploit the information that nature puts physics. Some familiar hypotheses are continental drift, the meteorite- at its disposal for evaluating hypotheses, and the character of that in- impact extinction of the dinosaurs, the big bang origin of the universe, formation differs, neither practice can be held up as more objective or and, more recently, the hypothesis that there are planets orbiting distant rational than the other. stars. What all of these hypotheses have in common is explaining observable phenomena (e.g., the complementary shapes of the east coast THE SCIENTIFIC METHOD of South America and the west coast of Africa, the iridium and shocked The hypotheses tested in classical experimental research are gen- quartz in the Cretaceous-Tertiary (K-T) boundary, the isotropic three- eral in character; ‘‘all copper expands when heated’’ provides a toy degree background radiation, the wobbling reflex motion of certain example. A conditional statement T (test implication) is inferred from stars) in terms of their past causes. As discussed herein, the use of a hypothesis H. T states what must happen if H is true. Test implica- computer simulations does not change their historical character. tions have the following form: if condition C (heating a piece of cop- Although the idea that all good scientists employ a single method for testing hypotheses is popular, an inspection of the practices of his- per) is brought about, then event E (the expansion of copper) will torical scientists and experimental scientists reveals substantial differ- occur. Test implications provide the basis for experiments. Condition ences. Classical experimental research involves making predictions and C is artificially produced in the laboratory, and investigators look for testing them, ideally in controlled laboratory settings. In contrast, his- an instance of E. torical research involves explaining observable phenomena in terms of How are hypotheses evaluated in light of the evidence obtained unobservable causes that cannot be fully replicated in a laboratory in an experiment? Under the rubric ‘‘the scientific method,’’ science setting. Many experimental scientists recognize this difference, and texts, from grade school through college, invariably provide one (or a identifying sound scientific practice with their own work, sometimes combination) of two accounts, scientific inductivism or falsificationism. denigrate the claims of historical scientists, contending that they can’t Scientific inductivism, commonly attributed to Francis Bacon, holds falsify their hypotheses or that their confirmatory arguments resemble that the occurrence of the predicted event E under condition C provides just-so stories (Rudyard Kipling’s fanciful stories, e.g., how leopards confirming evidence for H, and that if enough confirming evidence of got their spots). The startling number of physicists and chemists who the right sort is obtained, H should be accepted by the scientific com- attack the scientific status of neo-Darwinian evolution provides telling munity. Unfortunately, scientific inductivism runs afoul of the hoary examples of this phenomenon. The most trenchant criticism of histor- problem of induction: no finite body of evidence can conclusively es- ical science, however, comes from an editor of Nature, Henry Gee tablish a universal generalization. Faced with the problem of induction, (1999, p. 5, 8), who explicitly attacked the scientific status of all hy- many scientists embrace falsificationism, which holds that although potheses about the remote past; in his words, ‘‘they can never be tested hypotheses cannot be proved, they can be disproved. Unlike inductiv- by experiment, and so they are unscientific. No science can ever be ism, falsificationism receives support from logic. It utilizes a logically historical.’’ true inference rule called ‘‘modus tollens.’’ According to modus tol- 2001 Geological Society of America. For permission to copy, contact Copyright Permissions, GSA, or [email protected]. Geology; November 2001; v. 29; no. 11; p. 987–990. 987 lens, a generalization is false if it has at least one counterexample. The whether it was required for the successful result. While these responses hypothesis that all copper expands when heated is thus false if there to successful tests superficially resemble attempts at falsification, a lit- is a single case in which copper fails to expand when heated. Thus, tle reflection reveals that this can’t be what is going on, because they although one can never prove the hypothesis (because no amount of do not conform to Popper’s requirement that the tests performed be testing can rule out the possibility that a piece of copper will someday ‘‘risky.’’ The hypothesis has survived similar tests, and no one expects fail to expand when heated), it seems that it could be disproved. In it to fail this time. Even if it does, it won’t automatically be rejected. philosophical circles, falsificationism is associated with the work of Viewed from this perspective, the activity more closely resembles an Karl Popper (1963), who developed the logical insight about modus attempt to protect the hypothesis from misleading confirmations. In tollens into a sophisticated account of scientific practice. The basic idea other words, a close look at the work of experimental scientists sug- behind Popperian falsificationism is to subject a hypothesis to a ‘‘risky gests that they are primarily concerned with protecting their hypotheses test,’’ a test that, in the context of one’s background beliefs, is judged against false negatives and false positives, as opposed to ruthlessly highly likely to yield a disconfirming result. If the prediction fails, attempting to falsify them. This makes good sense because, as dis- modus tollens is invoked, and the hypothesis is ruthlessly rejected. cussed earlier, any actual test of a hypothesis involves many auxiliary According to falsificationism, it is unscientific to try to confirm a conditions that may affect the outcome of the experiment indepen- hypothesis. dently of the truth of the hypothesis. For more than 50 years philosophers have known that falsifica- In this light, let us turn to the reputedly problematic differences tionism is deeply flawed. There are two central difficulties. First, any between historical and experimental science. Historical scientists are actual experimental situation involves an enormous number of auxil- just as captivated by falsificationism as experimental scientists; as three iary assumptions about equipment and background conditions, not to eminent geologists (Kump et al., 1999, p. 201) counsel in a recent mention the truth of other widely accepted theories. When these con- textbook discussion of the extinction of the dinosaurs, ‘‘a central tenet ditions are taken into consideration, the logical inference licensed by of the scientific method is that hypotheses cannot be proved, only dis- modus tollens is radically altered. The falsity of an auxiliary assump- proved.’’ Nevertheless, there is little in the evaluation of historical hy- tion (versus the target hypothesis) could be responsible for

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