Blackstone organized the common law. He did so by structuring the law around rights and principles known in the natural-law tradition. This hitherto unknown cohesion commended common law to Americans at a Revolutionary moment when the rejection of common law—intellectually and politically—was possible, even likely. Recognizing today that a common-law legal system can be outlined and explained in reference to natural law is, itself, an achievement (given the broadly positivistic terrain of analysis of the common law). Blackstone offers an example, then, for how natural law can serve to describe the ultimate sources or justifications for human law as a system. But he does more. He offers natural-law tools for structuring the body of law and justifying or critiquing common law’s specific enactments, defenses, and punishments. Blackstone, however, does not merely apply natural law to common law. Whether we like the result or not, he suggests that, in matters of legal determination, human law is in conversation with natural law. And this conversation, he suggests, is not one in which natural law necessarily has the final word. One result is that natural law may explain and stabilize human laws while simultaneously rendering them contingent and revisable. Given the realities of sin, says Blackstone, human reason must be suitably modest in its claims to track natural law’s revelation of God’s reason and will.