(John Green) For over 50 years, constitutional scholars, and Supreme Court justices in particular, have used “penumbral reasoning” as one means to explain rulings expanding the Constitution of the United States. Law schools describe it as “reasoning by interpolation.” To put that in graphic terms, if you’re drawing a graph on paper, reasoning by interpolation allows you to extend the line off of the paper. I’m not a constitutional scholar, but I don’t think that’s necessary to see that this can lead to a very dark place.