The subject matter of comparison in comparative law is usually two or more legal systems (i.e. macro-comparison), or parts thereof (i.e. micro-comparison). Micro-comparison may be appropriate where the comparative study seeks to illustrate the varied responses within different legal systems to similar societal problems. However, determining what counts as a relevant similarity or difference for comparative purposes is at the heart of methodological issues in comparative law (Rosenfeld and Sajo, 2012).

There are various methods that scholars use to compare systems of constitutional law. One of the most commonly used methods is functional equivalence, which often begins by discovering the institution that deals with a social problem and then looking to other societies for legal (or other) institutions that deal with the same problem – in other words searching for a functional equivalent. Conversely, one may start with an institution in one society, ascertain its purpose or function, and then look for a functionally equivalent institution in another society. Given the plurality of methods available, however, the best way to choose the appropriate methodology is to look to the aims of the specific comparative study and ascertain what you hope to achieve. Palmer refers to this as a ‘sliding scale of methods’ in which the best approach will be adapted to the research.

Many of the tools needed to engage in the systematic study of constitutionalism across nations can be found in the social sciences, and comparative constitutional research benefits from the methodological approaches of other disciplines by allowing infrequently acknowledged features that form the backdrop of the constitutive laws of a place, such as culture and politics, to emerge (Hirschl, 2014).

Hirschl’s guiding principles

In determining the appropriate methodology for comparative constitutional research, Hirschl has recommended four guiding principles to follow:

• define the aim of the study (descriptive, taxonomical, explanatory and/or normative),
• articulate the study’s intended level of generalization and applicability (ranging from context-specific to universal and abstract),
• encourage methodological pluralism and analytical eclecticism when appropriate, and
• ensure a ‘rational, analytically adaptive connection’ between the research questions and the comparative method used.

Although the discussion takes place within the context of comparative constitutional law research, his approach may be easily adapted to other kinds of comparative law research.

Techniques

While experimental research, statistical analysis (large-N) and systematic examination of a small number of cases (small-N) are the major methods of causal inference and theory-testing in the study of politics and society, the majority of social science research in the area of comparative law has proceeded by way of ‘small-N’ studies (Hirschl, 2014).

Case studies offer the benefit of being able to see particular institutions or doctrines ‘in action’ within their own legal contexts. These can offer a different perspective than simply describing and translating foreign law or engaging in a straight comparison of rules. Focusing on case studies allows for a description of the ‘pathology’ of a legal system or the conflicts surrounding the application and interpretation of rules (Van Hoecke, 2015).

Although case studies can be used to explore a broad range of variables in a specific setting, they will also reduce your ability to form more general statements about the phenomenon being studied, due to the reduced number of comparable entities to validate findings (Jackson, 2012). This can be overcome by using structured comparative case studies, which narrow the analysis to a selected set of issues on a country basis to yield comparative perspectives on how similar issues are addressed in different constitutional systems.

Large-N studies might also provide a solution to the limited ability to generalise with single case studies or small-N research. These are particularly useful in considering broader trends in constitutionalism. Although large-N studies have been criticised as oversimplified and dismissive of qualitative or normative accounts, they are valuable to theory-building and testing in comparative constitutional studies and can provide exciting insights into trends that might otherwise be missed (Hirschl, 2014).