The variety of legal history published in general-interest law journals tends to differ from the variety published in history journals. This study compares the two varieties by examining footnote references in five general-interest law journals and footnote references in two journals of legal history. In the law journals, cases and statutes accounted for the single largest group of footnotes (approximately 35%), followed by references to other law journal articles (nearly 25%). In the legal history journals, these two categories accounted for less than 20% of all references; primary and secondary historical materials predominated in the footnotes. To be sure, legal decisions and law journal articles can also be historical sources: rather than being used as evidence of what the law is, they might be studied for what they reveal about legal reasoning or rhetoric in an earlier age. However, in most legal historical research that attends primarily to cases and statutes, these materials figure as evidence of the state of the law at that time. When the analysis relies on legal sources to trace the development of a certain doctrine and treats them as sufficient to account for that development, the result is the distinctive style of research that I seek to contrast against approaches that cast the net of historical inquiry more widely. To account for these different approaches, I suggest that law professors rely on a notion of proximate causation as a historiographic method. According to this approach, legal developments are proximately caused by other developments in the legal sphere, and other social and cultural developments play more attenuated roles, such that their influence is less significant. By proposing this explanation, I hope to draw more attention to assumptions about causation in legal historiography and to question their persuasive force.