Contemporary constitutional law and theory is preoccupied with the question of practice. Over the last decade, across a range of issues—from gun rights to elections to school prayer to the structure of the administrative state—the Supreme Court has decided cast on the basis of past practice. The Court and scholars have called this style of argument different names: historical gloss, constitutional liquidation, and history and tradition. Yet each does the same thing: explain when, how, and why past behavior should be legally relevant. They thus comprise a novel mode of constitutional interpretation that turns to history but in search of practical, rather than linguistic, meaning.

Yet historical gloss, constitutional liquidation, and history and tradition have not been recognized as a coherent category, let alone studied in a systematic way. Instead, they have largely developed in isolation. This Article provides an important corrective. It terms these views “historical practice theories” and advances a unified account that explains their common structure, foundations, and tensions.

The Article makes three claims. The first, descriptive claim is that theories share a four-part structure: application conditions, units of account, interpretive weight, and normative rationales. The second claim is constructive. Two of these theories—gloss and liquidation—aim to achieve descriptive fidelity to current practice by aligning the law with it. This descriptive fidelity, in turn, renders them more intelligible as accounts of constitutional law and counts as a normative reason to endorse them. The final claim observes three conceptual ironies. First in pursuing descriptive fidelity, historical practice theories introduce considerable judicial discretion, the limitation of which is a central aim of constitutional theory. The second irony is that despite the concessions gloss and liquidation make to understand the past, they fall short in satisfying the demands of both historical and legal interpretation. The final irony is that gloss and liquidation are better understood as deference regimes rather than substantive theories of interpretation, since they instruct judges to respect the considered constitutional views of other actors rather than impose their own views. This Article thus deepens our understanding of an important, novel form of unwritten constitutionalism.