This special issue of Political Analysis engages in a dialogue between qualitative and quantitative methods. It proposes that each has something to say to the other and more generally has a contribution to make to empirical social science.

The quantitative and qualitative research traditions can be thought of as distinct cultures marked by different values, beliefs, and norms. In this essay, we adopt this metaphor toward the end of contrasting these research traditions across 10 areas: (1) approaches to explanation, (2) conceptions of causation, (3) multivariate explanations, (4) equifinality, (5) scope and causal generalization, (6) case selection, (7) weighting observations, (8) substantively important cases, (9) lack of fit, and (10) concepts and measurement. We suggest that an appreciation of the alternative assumptions and goals of the traditions can help scholars avoid misunderstandings and contribute to more productive “cross-cultural” communication in political science.

This article discusses the application of qualitative methods in analyzing causal complexity. In particular, the essay reviews how process tracing and systematic case comparisons can address path-dependent explanations. The article unpacks the concept of path dependence and its component elements of causal possibility, contingency, closure of alternatives, and constraints to the current path. The article then reviews four strengths that case studies bring to the study of path dependence: offering a detailed and holistic analysis of sequences in historical cases, being suitable for the study of rare events, facilitating the search for omitted variables that might lie behind contingent events, and allowing for the study of interaction effects within one or a few cases.

Political scientists overwhelmingly seek evidence of causation by measuring changes in the mean of the distribution of the dependent variable. This article points out that some causal relationships produce changes in the variance, not the mean, of that distribution. It makes the case for variance-altering causation by demonstrating its empirical relevance to political scientists. The article also lays out an array of causal mechanisms—under the general headings of aggregation, contagion, and constraint—in order to demonstrate the logical coherence of variance-altering causation and the many ways in which it can arise. The discussion highlights the often-stringent empirical and logical requirements that must be met if the researcher hopes to make concrete predictions about changes in variance.

Because of its inherently asymmetric nature, set-theoretic analysis offers many interesting contrasts with analysis based on correlations. Until recently, however, social scientists have been slow to embrace set-theoretic approaches. The perception was that this type of analysis is restricted to primitive, binary variables and that it has little or no tolerance for error. With the advent of “fuzzy” sets and the recognition that even rough set-theoretic relations are relevant to theory, these old barriers have crumbled. This paper advances the set-theoretic approach by presenting simple descriptive measures that can be used to evaluate set-theoretic relationships, especially relations between fuzzy sets. The first measure, “consistency,” assesses the degree to which a subset relation has been approximated, whereas the second measure, “coverage,” assesses the empirical relevance of a consistent subset. This paper demonstrates further that set-theoretic coverage can be partitioned in a manner somewhat analogous to the partitioning of explained variation in multiple regression analysis.

In this paper, we argue that claims of necessity and sufficiency involve a type of asymmetric causal claim that is useful in many social scientific contexts. Contrary to some qualitative researchers, we maintain that there is nothing about such asymmetries that should lead scholars to depart from standard social science practice. We take as given that deterministic and monocausal tests are inappropriate in the social world and demonstrate that standard multiplicative interaction models are up to the task of handling asymmetric causal claims in a multivariate, probabilistic manner. We illustrate our argument with examples from the empirical literature linking electoral institutions and party system size.

Social scientists who strive to reflect on their research “while they're doing it” (Becker 1998) live in very fortunate times. On the one hand, it seems as if an increasing number of scholars want to do a little more than simply apply ready-made recipes. On the other hand, a few key volumes have recently been published that move beyond ready-made recipes. In my personal top three, I would most probably place Mahoney and Rueschemeyer (2003), George and Bennett (2005), and—last but not least—the volume discussed in this symposium. What distinguishes Rethinking Social Inquiry (RSI) from the two other volumes, in my view, is that it has a broader agenda and hence a broader ambition.

Every good book has a small bit—a sentence, paragraph, maybe a page—that the authors intended as a simple aside but which brings an epiphany to the reader. In Brady and Collier (2004), this occurs at the beginning of chapter 3: Brady's critique of the “quantitative template,” where the recovering seminarian frames our discourse on the philosophy of social inquiry in terms of pragmatic theology and homeliletics, rather than science or sociology. Hey, that is it!—while this debate is not in any sense about religion, its dynamics are best understood as though it were about religion. We have always known that, it just needed to be said.

Rethinking Social Inquiry (RSI) is a key turning point in a long arc of development and contestation within and between qualitative and quantitative research methods in the social sciences. It builds on and further advances three important trends in these research methods: a renaissance in qualitative methods in the last decade, the continuing refinement of statistical and formal methods, and a nascent convergence of methodologists of all kinds behind a more pluralistic vision of methodology that includes growing interest in multimethod work. RSI achieves these contributions not just substantively but symbolically, bringing together leading methodologists in the quantitative and qualitative traditions, most notably the editors themselves, to address the tough issue of what would constitute shared standards for good research regardless of method. Although much of the initial commentary on RSI will no doubt focus on its critiques of Designing Social Inquiry, I suspect that in the long run the subtitle of RSI (“Diverse Tools, Shared Standards”) better captures what will be its lasting contribution to the social sciences.

This book, responding to the stimulus of the volume by Gary King, Robert Keohane, and Sidney Verba, helps to carry forward King et al.'s original purpose—to bridge quantitative and qualitative perspectives and find the unity of method underlying both of them. Whether or not we accept King et al.'s own vision of the underlying unity, it is clear that their work has been a catalyst for progress in this direction.

When I first read King, Keohane, and Verba (1994) (KKV), I was excited by the general theme of what seemed to me the obvious, but usually unspoken, idea that all political scientists, both quantitative and qualitative, are scientists and governed by the same scientific standards. KKV, as Henry Brady (Brady and Collier 2004, chap. 3) cleverly notes, clearly were preaching to the qualitative researcher, and the subject of the sermon was that qualitative researchers should adopt many of the ideas standard in quantitative research. Thus, to abuse both the metaphor and KKV, one might compare KKV to the view of the Inquisition that we are all God's children. But, having sat through many talks based on case studies, it is clear to me that getting everyone to think about the nature of the scientific enterprise we are all engaged in can only be a good thing.

The discussion of qualitative and quantitative research methods in political science has followed a “long arc of development,” according to Andrew Bennett (this symposium). He sees our book Rethinking Social Inquiry: Diverse Tools, Standards (RSI) as a “key turning point” in this development and as contributing to a more pluralistic vision of methodology. We would certainly be gratified if we have indeed made this contribution. Yet this is an ongoing discussion, and this symposium points to fruitful directions this discussion can take.