ABSTRACT
Some concepts are difficult to define, yet we still “know” what they mean. This was the point of Justice Potter Stewart’s opinion in Jacobellis v. Ohio, which included the assertion that “I shall not today attempt further to define the kinds of material I understand to be embraced within that shorthand description [hard-core pornography]; and perhaps could never succeed in intelligibly doing so. But I know it when I see it, and the motion picture involved in this case is not that.”
