Abstract: In the middle of the twentieth century, legal realist Karl Llewellyn largely persuaded the legal community that the canons of construction are indeterminate, and judges use them to justify reasoning by other means. Toward the end of the twentieth century, however, the canons enjoyed a strong revival, both with the federal judiciary and across a surprisingly broad range of legal academies. This essay offers a hypothesis about the canons’ revival. Llewellyn is justly regarded as a lion of the realist movement, and his critique of the canons is one of the most influential realist works of the last century. But the early success of his critique may, in fact, relate to the declining post-World War II fortunes of legal realism in statutory interpretation theory. In the same period in which he made his critique of the canons, most judges and legal scholars came to the view judges could meaningfully resolve textual ambiguity by consulting the legislature's intent or purpose, to be derived in no small part from legislative history. Conversely, the impact of Llewellyn’s critique of the canons impact began to wane in the 1980s, when influential textualist and pragmatist scholars revived (for quite different reasons) broader realist claims about the inaccessibility and unreliability of legislative intent or purpose as organizing principles in statutory construction. In economists' terms, canons of construction and intent or purpose may be substitutes, rather than complements, in determining statutory meaning. On that view, the canons' revival may simply be the flip side of the growing perception that the early realists were correct in arguing that it is hard to get inside “Congress's mind.” The essay elaborates on this point and then briefly suggests preliminary implications of this conclusion.