Where does penumbra collide?

In legal philosophy the penumbra is the zone of uncertainty around the settled core of a rule: a general term has clear central cases to which it plainly applies (the core) and a surrounding band of borderline cases where its application is genuinely contestable (the penumbra). Hart's 1958 Positivism and the Separation of Law and Morals used this core-and-penumbra picture to describe the "open texture" of legal language and to argue that penumbral cases call for judicial choice rather than mechanical deduction. The referent is the indeterminate margin of a concept's application in adjudication: a feature of language and interpretation, not a shadow of light or a ring of injured tissue.[1]

Unit

The range of borderline cases where a rule's application is genuinely contestable

Recovery means

Not applicable

Measured by

Identified by disagreement among competent interpreters over whether a term applies to a borderline case

In clinical medicine the ischemic penumbra is the ring of brain tissue around the dead core of a stroke that is electrically silent and functionally impaired but still structurally alive, kept marginally perfused so that it can be rescued if blood flow is restored quickly, or lost to the infarct if it is not. Astrup, Siesjö, and Symon's 1981 Thresholds in cerebral ischemia - the ischemic penumbra defined this region by two flow thresholds: one below which function fails and a lower one below which the tissue dies. The referent is a salvageable at-risk zone bordering an infarct core, measured by cerebral blood flow and imaging, distinct from a sunspot's fringe or a rule's borderline cases.[2]

Unit

The volume of hypoperfused but still-viable tissue around an infarct core

Recovery means

Reperfusion within the therapeutic window can restore the penumbra to function; without it the tissue is recruited into the infarct

Measured by

Delineated by cerebral blood flow thresholds and by perfusion-diffusion mismatch on imaging