To be a lawyer, Coke believed, was to understand the law as rational: to grasp the function of particular rules in the light of their place in the system as a whole. This understanding had the disadvantage that it was legal not historical; Coke claimed, no doubt quite seriously, to reconstruct intentions behind particular rules, but his view of the past was dictated by his professional presuppositions. A theory of the common law as reason greatly discouraged any sense that its origins were messily contingent. In depicting law as rational (that is, in understanding it as law) he denied its actual roots in arbitrary arrangements entered into by consent. Hale's great achievement, as a legal thinker, was to combine Coke's insights into the character of common law with a genuinely historical perspective. His starting point, in this and other areas, was his friend Selden's (1588–1654) thought.

John Selden was a barrister, and earned some money by conveyancing, but he was really, by the time Hale knew him, a professional antiquarian with a passion for the law. His trenchant Table talk, from the period of their friendship, gives a sense of his vigorous mind. His interests were bafflingly various, embracing jurisprudence, history, and all the oriental languages which were at that time studied in the West, but there was nonetheless a common concern. The law of particular places, created by local consent, was defended against rival codes with universal claims.