Penumbra (law)

In United States constitutional law, the penumbra includes a group of rights derived, by implication, from other rights explicitly protected in the Bill of Rights. These rights have been identified through a process of "reasoning-by-interpolation", where specific principles are recognized from "general idea[s]" that are explicitly expressed in other constitutional provisions. Although researchers have traced the origin of the term to the nineteenth century, the term first gained significant popular attention in 1965, when Justice William O. Douglas's majority opinion in Griswold v. Connecticut identified a right to privacy in the penumbra of the constitution.

Commentators disagree about the precise origin of the use of the term penumbra in American legal scholarship, but most believe it was first used in the late nineteenth century. Burr Henly, for example, traces the first use of the word to an 1873 law review article written by Oliver Wendell Holmes, in which he argued that it is better for new law to grow "in the penumbra between darkness and light, than to remain in uncertainty". Luis Sirico and Henry T. Greely, on the other hand, trace the term to Justice Stephen Johnson Field's 1871 circuit court opinion in Montgomery v. Bevans, where Justice Field used the term to describe a period of time in which it was uncertain whether an individual could legally be considered deceased. Other commentators, including Glenn H. Reynolds and Brannon P. Denning, note that elements of penumbral reasoning can be found in much older cases that precede the first use of the term penumbra; they trace the origins of penumbral reasoning to United States Supreme Court cases from the early nineteenth century. For example, Reynolds and Denning describe Chief Justice John Marshall's opinion in McCulloch v. Maryland as "the quintessential example of penumbral reasoning".

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