This is a study of Justice Oliver Wendell Holmes Jr.’s original contribution to both legal logic and general logical theory. Conventional legal logic has focused on the operation of judges deciding the immediate case. Holmes (from analogies with natural science) came to understand law as an extended process of inquiry into recurring problems. The role of the legal profession is thereby recast by Holmes to recognize the importance of input from outside the law—the importance of the social dimension of legal and logical induction. Lawyers and judges perform an important but often largely ancillary role, one that must nevertheless be evaluated from the standpoint of a logical method prioritizing experience over general propositions. Addressing the nature of the difficult case, Holmes emphasized an aspect of uncertainty distinct from that commonly envisioned for the deciding judge. Rather than unclarity or contradiction within the settled law, or vagueness in the meaning or application of an applicable rule, Holmes focused instead on the relation of a novel or unanticipated fact to an underlying and emergent social problem. The appearance of legal uncertainty, where opinions and authorities are sharply divided in a controversial case, signals the early stage of a broader social continuum of inquiry. It is not then strictly a legal uncertainty, and it is a mistake to expect that judges alone can immediately resolve the larger problem.