What Is the Role of Induction and Deduction in Reasoning and Scientific Inquiry?

A long-standing and continuing controversy exists regarding the role of induction and deduction in reasoning and in scientific inquiry. Given the inherent difficulty in reconstructing reasoning patterns based on personal and historical accounts, evidence about the nature of human reasoning in scientific inquiry has been sought from a controlled experiment designed to identify the role played by enumerative induction and deduction in cognition as well as from the relatively new field of neural modeling. Both experimental results and the neurological models imply that induction across a limited set of observations plays no role in task performance and in reasoning. Therefore, support has been obtained for Popper’s hypothesis that enumerative induction does not exist as a psychological process. Instead, people appear to process information in terms of increasingly abstract cycles of hypothetico-deductive reasoning. Consequently, science instruction should provide students with opportunities to generate and test increasingly complex and abstract hypotheses and theories in a hypothetico-deductive manner. In this way students can be expected to become increasingly conscious of their underlying hypothetico-deductive thought processes, increasingly skilled in their application, and hence increasingly scientifically literate. 2005 Wiley Periodicals, Inc. J Res Sci Teach 42: 716–740, 2005 In the words of the American Association for the Advancement of Science (1989), ‘‘teaching should be consistent with the nature of scientific inquiry’’ (p. 147). Unfortunately, for teachers wanting to do so, controversy persists among scholars regarding the nature of scientific inquiry and its underlying reasoning patterns. For example, Allchin (2003) paints scientific inquiry as ‘‘ . . . a combination of blind search and selection, and limited induction . . . ’’ whereas Lawson (2003a) counters that scientific inquiry is driven by cycles of hypothetico-deductive reasoning. The recent Allchin/Lawson exchange represents simply another volley in a continuing epistemological battle that can be traced to Greek antiquity. To provide a better sense of this long-standing battle, consider the following list of contrasting claims made by several notable logicians, philosophers, and scientists. Although the list is fairly lengthy, the views expressed are striking, not only because they represent Contract grant sponsor: National Science Foundation; Contract grant number: DUE 9453610. Correspondence to: A.E. Lawson; E-mail: [email protected] DOI 10.1002/tea.20067 Published online 2 May 2005 in Wiley InterScience (www.interscience.wiley.com). 2005 Wiley Periodicals, Inc. such opposing claims, but because they are so boldly expressed by so many presumed experts. We start with claims clearly favoring induction’s role in science. These claims are followed by those that question induction’s role, by those that even question induction’s psychological existence, and by those that clearly view science as hypothetico-deductive in nature. Claims favoring induction’s role include: The basic idea behind inductive reasoning is that of learning from experience. We notice patterns, resemblances, or other kinds of regularities in our experiences, some quite simple (sugar sweetens coffee), some very complicated (objects move according to Newton’s laws), and we project them onto other cases. We use inductive reasoning so frequently in everyday life that the inductive nature of this kind of conclusion drawing regularly goes unnoticed. (Tidman & Kahane, 2003, p. 6) In induction the scientist goes out and measures aspects of the phenomenon under study. Then those measurements are analyzed and generalizations, also called theories, are made from the analyses. Charles Darwin caught many finches on the Galapagos Islands. He later noticed that the shapes of the birds’ beaks were different on each island. After studying the beaks, he concluded that each shape seemed to serve a purpose suited to the conditions on a particular island. . . .Darwin developed a theory that at some time in the past, one type of finch arrived at the islands and then evolved differently on each island . . . he later extended this theory of evolution to all life forms; thus the most important theory in the biological sciences was developed using inductive reasoning; data collection–analysis–theory. (Lee, 2000, p. 15) How do humans in general and scientists in particular learn about the nature of the world? Clearly, some process of induction is involved. Associations, patterns, regularities are observed, and on this basis expectations or concepts regarding the way the world is organized is formed. Whether or not deductive logic plays a role in scientific thinking, inductive reasoning is clearly central to what scientists do. (Kuhn, Amsel, & O’Loughlin, 1988, p. 21) Mendel’s ‘law of hybridization’ thus seems to follow in a tradition of framing basic laws: mathematical regularities of nature, such as Snel’s Law of Refraction or Boyle’s Law of Gases. One may note that these laws originate as empirical generalizations. No theory or concept—or specific prediction or expected result—guided their discovery. Rather they exemplify plain arithmetic analysis and enumerative induction . . . . No overarching hypothetico-deductive method seems to have guided Mendel’s discovery of his law of dihybrid development. Rather, it was a combination of blind search and selection, and limited induction across a number of cases with similar arithmetic patterns. (Allchin, 2003,