What does the word 'penumbra' mean in this sentence?

Question

The following is an extract from the book The Road to Serfdom. I was wondering what 'penumbra' is used to convey in the sentence.

There is no restrictive penumbra of individual rights that can never be touched by government in administrative matters whatever the circumstances.

A quick Google search defines penumbra as:

the partially shaded outer region of the shadow cast by an opaque object.

Astronomy
the shadow cast by the earth or moon over an area experiencing a partial eclipse.
Astronomy
the less dark outer part of a sunspot, surrounding the core.

1. a peripheral or indeterminate area or group. "an immense penumbra of theory surrounds any observation"

Answer 1

Literally it means a shadow, or more specifically the a partial shadow at the edge of a shadow, from paene (almost, nearly) and umbra (shadow).

In legal theories about rights and powers, penumbra means a right or set of rights that is implied by a formally stated right, or powers that are implied by a law.

The legal definitions are not firm or well-defined, as they come from figurative uses by a relatively small number of findings in terms of US federal law. The best known is Justice Arthur Goldberg's Opinion of the Court in Griswold v. Connecticut 1965. Here he used the term several times, most famously in:

The foregoing cases suggest that specific guarantees in the Bill of Rights have penumbras, formed by emanations from those guarantees that help give them life and substance.

This not only had the specific case of demonstrating a right to privacy as entailed in the Bill of Rights, and by extension rule Connecticut ban on contraceptives unconstitutional, but had a strong influence on later legal thinking that affected some particularly controversial cases (Roe v. Wade 1973, perhaps the most so).

The figurative use though goes back earlier, to Montgomery v. Bevans 1871.

Being a figurative use, the exact meaning has differed in different cases, but "right that is implied by another right" is a good rough definition.

Answer 2

In legal writing (especially academic or appeals-court legal writing) "penumbra" is sometimes used to refer to a scope of a right that extends perhaps a bit beyond what that right has historically applied to, or extends beyond what the literal language specifying the right says.

It's like the current state of the particular right, as understood or written, casts a shadow behind it (as in the astronomy context) that also provides some level of protection from, for example, government intrusion or action.

It is perhaps most famously stated in U.S. law in Griswold vs. Connecticut, 381 U.S. 479 (1965), in which the U.S. Supreme Court held that a right to privacy, while not literally stated in the Constitution, existed in the "penumbras" of other Constitutional protections.