“I know it when I see it” comes from Justice Potter Stewart’s concurring opinion in Jacobellis v. Ohio, a 1964 U.S. Supreme Court case about whether a French film could be banned as obscene. Stewart used the phrase to admit that hard-core pornography might be impossible to define in precise legal terms while insisting that judges could still recognize it when they encountered it. The line became one of the most quoted sentences in American legal history, and it captured a real frustration: by 1964, the Court had spent seven years trying to write a workable definition of obscenity, and no majority could agree on one.
The Case That Produced the Line
Nico Jacobellis managed a movie theater in Cleveland Heights, Ohio. He screened Les Amants (“The Lovers”), a 1958 film directed by Louis Malle and starring Jeanne Moreau as a bored wife who leaves her husband after an affair with a younger man. The film contained a love scene considered frank for its time and had been censored or challenged in several countries.1Library of Congress. 378 U.S. 184 Jacobellis v. Ohio
Ohio charged Jacobellis with possessing and exhibiting an obscene film. He was convicted on two counts and fined $500 on the first and $2,000 on the second. The Ohio Supreme Court upheld the conviction, and he appealed to the U.S. Supreme Court.
The Court reversed, but the decision was badly fractured. No single opinion commanded a majority. Justice Brennan wrote the lead opinion, joined only by Justice Goldberg. Justices Black and Douglas filed their own. Goldberg wrote separately again. Stewart’s concurrence ran about two paragraphs.2Justia. Jacobellis v. Ohio, 378 U.S. 184 (1964) Chief Justice Warren and Justices Clark, Harlan, and White dissented. The splintering itself told a story: even when the justices could agree on a result, they could not agree on a reason.
What Stewart Actually Wrote
Stewart began his concurrence by acknowledging the Court’s prior attempts to define obscenity and noting that the governing precedent could be read in multiple ways. He then stated his own position: criminal obscenity laws, under the First and Fourteenth Amendments, should reach only hard-core pornography. The famous sentence followed:
“I shall not today attempt further to define the kinds of material I understand to be embraced within that shorthand description, and perhaps I 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.”2Justia. Jacobellis v. Ohio, 378 U.S. 184 (1964)
That was essentially the entire opinion. Stewart offered no multi-factor test, no list of features, no explanation of where the line fell. He simply declared that The Lovers was on the protected side of it. The brevity was the point.
The Frustration Behind the Concession
Before Stewart’s line, the Court’s primary obscenity framework came from Roth v. United States (1957). Roth held that obscene material falls outside First Amendment protection and offered a test: whether the average person, applying contemporary community standards, would find that the dominant theme of the material as a whole appeals to a “prurient interest” in sex.3Justia. Roth v. United States, 354 U.S. 476 (1957)
Roth tried to separate protected sexual expression from punishable obscenity, but it generated more questions than answers. What counted as “prurient interest”? Whose community standards? How much was too much? Over the next seven years, the justices issued a string of fractured decisions, often reversing obscenity convictions without agreeing on why. Lower courts had almost no reliable guidance. That was the situation Stewart walked into. After watching his colleagues try and fail to write a definition that would hold, he decided honest imprecision was better than false precision.
Why Intuition Failed as a Standard
Stewart’s approach had an obvious appeal. Visual material triggers responses that are difficult to capture in legal prose, and any definition specific enough to be useful risks being either too broad, sweeping in legitimate art, or too narrow, letting genuinely exploitative material slip through. His instinct was that judges, as educated members of the community, could look at the material and reach a reasonable conclusion.
The problems were just as obvious. Different judges have different thresholds. A standard that depends entirely on who happens to be sitting on the bench is not really a standard. It offers no guidance to filmmakers, publishers, or prosecutors trying to figure out in advance whether particular material is legal. And it concentrates enormous power in individual judges, with no meaningful way to review their reasoning on appeal, because the reasoning is, by design, unexplained.
Two theater managers showing the same film in different courthouses could face opposite outcomes, with no doctrinal basis for distinguishing the cases. For a constitutional right, that level of unpredictability is hard to justify. Most critics landed in the same place: not that Stewart was wrong about the difficulty of definition, but that “I know it when I see it” is a confession dressed up as a rule.
How the Court Moved On: Miller v. California
The Court replaced the fragmented standards of the Stewart era in 1973 with Miller v. California. Chief Justice Burger’s majority opinion modified Roth and produced a three-part framework still in use today.4Justia. Miller v. California, 413 U.S. 15 (1973) Material can be classified as legally obscene only if all three conditions are met:
- The average person, applying contemporary community standards, would find the work as a whole appeals to a prurient interest in sex.
- The work depicts sexual conduct in a patently offensive way, as specifically defined by the applicable state law.
- The work as a whole lacks serious literary, artistic, political, or scientific value.
The third prong is sometimes called the SLAPS test after its initials. It replaced the earlier “utterly without redeeming social value” standard from Memoirs v. Massachusetts, which had been nearly impossible for prosecutors to meet.5Library of Congress. Miller v. California Under Miller, prosecutors no longer need to prove a work is utterly worthless, only that it lacks serious value in any of those four categories.
All three prongs must be satisfied before criminal liability attaches. A sexually explicit film with genuine artistic merit is protected. A work that offends community standards but does not depict sexual conduct as defined by state law is protected. Miller does not eliminate subjectivity, but it gives courts, prosecutors, and creators a structured framework that Stewart’s approach deliberately avoided.
Why the Phrase Endures
Stewart’s six words survive not because they solved the obscenity problem but because they named it. The phrase captures a situation almost everyone has encountered: you recognize something immediately but cannot explain your criteria to someone who disagrees. It has migrated well beyond obscenity law, invoked whenever people debate concepts that resist precise definition, from what counts as “art” to what qualifies as “fake news.”
Within legal circles, the phrase functions more as a cautionary tale than a triumph. It represents the moment a Supreme Court justice conceded that the law’s most powerful tool, language, was not up to the task. Miller eventually gave lower courts the structured replacement they needed, but even Miller did not eliminate the subjectivity that frustrated Stewart. The “average person” and “contemporary community standards” are themselves open to interpretation, and the SLAPS value inquiry still requires the kind of judgment call Stewart was honest enough to admit he was making. The difference is that Miller forces judges to show their work. Stewart’s enduring contribution was showing, perhaps unintentionally, why that matters.