Investigating the Psychological World: Scientific Method in the Behavioral Sciences

5. Theory Appraisal: Inference to the Best Explanation

5 Theory Appraisal: Inference to the Best Explanation If the fact that a theory provides the best available explanation for some important phenomenon is not a justification for believing that the theory is at least approximately true, then it is hard to see how intellectual inquiry could proceed. —Richard Boyd (1984, 67) 5.1 Introduction Contemporary scientific methodology boasts a number of general approaches for evaluating scientific theories. Prominent among these are the hypothetico-deductive method, which evaluates theories in terms of predictive success; Bayesian accounts of confirmation, which assign probabilities to hypotheses using Bayes’s theorem; and inference to the best explanation, which accepts theories when they are judged to provide better explanations of the evidence than their rivals do. These are three of the four major theories of scientific method canvassed in chapter 1. Because of its focus on procuring descriptive generalizations, the simple inductive account of scientific method does not seriously address the matter of theory appraisal. It has been stated repeatedly that the hypothetico-deductive method is by far the most widely used approach to theory appraisal in psychology (see, e.g., Rorer, 1991; Rozeboom, 1997). Despite some urgings (e.g., Edwards, Lindman, & Savage, 1963; Lee & Wagenmakers, 2005; Dienes, 2011), psychologists have been reluctant to use Bayesian statistical methods to test their research hypotheses and theories. They have mostly preferred to use classical statistical significance testing within a hypothetico -deductive framework. Unfortunately, inference to the best explanation has received almost no attention by psychological researchers. 106 Chapter 5 Many scientists in the natural and biological sciences have placed stock in the explanatory standing of theories, with Darwin and Einstein prominent among them (Janssen, 2002). In a well-known passage in the final chapter of On the Origins of Species, Darwin declares his confidence in justifying theories by appeal to explanatory considerations: It can hardly be supposed that a false theory would explain, in so satisfactory a manner as does the theory of natural selection, the several large classes of facts above specified [e.g., the geographical distribution of species, the sterility of hybrid species]. It has recently been objected that this is an unsafe method of arguing. But it is a method used in judging common events of life, and has often been used by the greatest natural philosophers. The undulatory theory of light has thus been arrived at; and the belief of the revolution of the earth on its own axis was until lately supported by hardly any direct evidence. (Darwin, 1958, 452) It is clear that Darwin set great store by the fact that his theory of natural selection provided a much better explanation of the classes of facts such as those just mentioned than did the rival creationist theory. In addition, methodologists have been concerned for some time to articulate ways in which we can understand the explanatory worth of theories (e.g., Lipton, 2004; Josephson & Josephson, 1994; Thagard, 1989, 1992). However, although inference to the best explanation (IBE) is used in some sciences and extensively discussed in the philosophy of science, it is seldom heard of in psychology. This is an omission that I believe needs to be put right. The primary purpose of this chapter is to bring the important idea of IBE to the attention of psychologists while emphasizing that the literature on the topic contains methodological resources that can help researchers evaluate the explanatory worth of their theories (Haig, 2009). I begin by introducing the general idea of explanatory inference. Then I consider a number of different approaches to characterizing IBE; prominent among these is the theory of explanatory coherence , which is the approach to theory appraisal adopted by ATOM. Thereafter I discuss the strengths and limitations of IBE, together with its relationship to other major approaches to theory appraisal and its place in the broader domain of scientific inference. The chapter’s penultimate section considers IBE in relationship to psychology, and in the conclusion, I recommend that psychologists use IBE as an appropriate means of evaluating the worth of their explanatory theories. Theory Appraisal 107 5.2 Inference to the Best Explanation In accordance with its name, IBE is based on the idea that much of what we know about the world, in both science and everyday life, is based on considerations of explanatory worth. Scientists often accept theories about the hidden causes of empirical phenomena because they believe them to be the best explanations of...