I know it when I see it

Based on Wikipedia: I know it when I see it

The Six Words That Haunted a Supreme Court Justice

In 1981, Supreme Court Justice Potter Stewart made a rueful confession. Of all the carefully reasoned opinions he had written across decades on the nation's highest court, he knew exactly which words would follow him to the grave: "I know it when I see it."

He was right. Those six words, scribbled into a short concurrence back in 1964, became one of the most quoted phrases in American legal history. They appear in law school textbooks, philosophy seminars, and countless dinner party arguments about the nature of knowledge itself. Stewart had intended them as a modest admission of limitation. Instead, they became his immortal epitaph.

The irony is that Stewart never actually used the word "obscenity" in that famous passage. What he claimed to recognize on sight was something more specific: "hard-core pornography." But the phrase escaped its original context almost immediately, becoming shorthand for any situation where someone claims to recognize something important without being able to define it precisely.

The Case That Started It All

The year was 1964. The case was Jacobellis versus Ohio, and at its center was a French film called "The Lovers," directed by Louis Malle. A Cleveland Heights movie theater manager named Nico Jacobellis had been convicted of possessing and exhibiting an obscene film. Ohio courts agreed the movie crossed a line. The question before the Supreme Court was whether that line existed at all under the Constitution.

The majority ruled in Jacobellis's favor. The film was not obscene, they decided, and therefore the First Amendment protected it. Justice Stewart agreed with this conclusion but took a different path to get there.

His concurrence was remarkably brief. He acknowledged that the Court had been struggling for years to articulate exactly what separated protected speech from unprotected obscenity. Criminal obscenity statutes, he noted, were limited to "hard-core pornography." And then came the confession that would define his legacy:

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.

It was an admission of defeat dressed up as pragmatism. Stewart was essentially saying: I cannot give you a definition that would survive logical scrutiny. I cannot hand you a formula. But I can tell you that whatever pornography is, this French art film isn't it.

Why Defining Obscenity Proved So Impossible

To understand why Stewart threw up his hands, you need to appreciate the conceptual quicksand the Supreme Court had been wading through for nearly a century.

The trouble starts with a deceptively simple question: What makes something obscene? Not just offensive or distasteful—obscene in a way that forfeits constitutional protection. The First Amendment generally prevents the government from censoring speech, but the courts have long recognized exceptions. You cannot falsely shout "fire" in a crowded theater. You cannot publish military secrets during wartime. And you cannot, the courts agreed, distribute truly obscene material.

But what counts as "truly obscene"?

For decades, American courts imported a standard from Victorian England. A 1868 case called Regina versus Hicklin established that material was obscene if it could "deprave and corrupt those whose minds are open to such immoral influences." This was extraordinarily broad. Taken literally, it meant that anything capable of corrupting the most susceptible reader—a child, perhaps, or someone already inclined toward immorality—could be banned entirely.

The Hicklin standard allowed prosecutors to suppress serious literature alongside genuine smut. James Joyce's "Ulysses" was banned under its logic. So were works by D.H. Lawrence, Henry Miller, and countless others. The test asked not whether the average reader would be corrupted, but whether any reader might be.

The Roth Test: A First Attempt at Precision

In 1957, the Supreme Court tried to bring some sanity to the situation with Roth versus United States. Justice William Brennan, writing for the majority, rejected the Hicklin approach. The new test focused on the "average person, applying contemporary community standards." Material was obscene only if its "dominant theme taken as a whole appeals to the prurient interest."

This was progress. The phrase "taken as a whole" meant that a book couldn't be banned because of a single steamy passage. The focus on "average" people and "community standards" meant that material couldn't be suppressed just because it might corrupt the unusually susceptible. And "prurient interest"—meaning a shameful or morbid interest in sex—was at least attempting to distinguish between legitimate artistic depictions of sexuality and material designed purely to titillate.

But the Roth test created new problems. What exactly were "contemporary community standards"? Which community? A cosmopolitan neighborhood in Manhattan might have very different standards than a rural town in Mississippi. And who was this hypothetical "average person"? How prudish or permissive should we imagine them to be?

More fundamentally, the Roth test offered no protection for material that might be artistically valuable but still appealed primarily to prurient interest. A brilliantly written novel exploring human sexuality could theoretically be suppressed if its "dominant theme" was too provocative.

The Justices Go to the Movies

Here is where the story takes a surreal turn. Unable to agree on clear legal standards, the Supreme Court justices started watching the allegedly obscene films themselves in the Court's basement screening room. These sessions became known, with dark humor, as "Movie Day at the Supreme Court."

Justice Thurgood Marshall reportedly attended only once. Justice Hugo Black attended but closed his eyes—he believed the First Amendment provided absolute protection and saw no need to evaluate the material's content. Justice John Harlan II, whose eyesight was failing, had his clerks narrate what was happening on screen.

The scene is almost comic: nine of the nation's most distinguished legal minds, gathered in a darkened room, squinting at grainy footage and trying to determine whether what they were seeing crossed some ineffable line. No wonder Stewart concluded that he might never succeed in articulating an intelligible definition. The enterprise seemed to resist definition by its very nature.

The Miller Test: Final(ish) Answers

The Court kept trying. In 1966, Memoirs versus Massachusetts added a new requirement: material had to be "utterly without redeeming social value" to be obscene. This seemed like a victory for free expression—surely almost anything could claim some tiny sliver of social value—but it created its own absurdities. Pornographers began including pseudo-educational introductions or tacking on "redeeming" epilogues to immunize their work from prosecution.

Finally, in 1973, Miller versus California established what remains the governing standard today. The Miller test requires all three of the following conditions to be met before material can be banned as obscene:

• The average person, applying contemporary community standards, would find that the work, taken as a whole, appeals to the prurient interest.
• The work depicts or describes, in a patently offensive way, sexual conduct specifically defined by applicable state law.
• The work, taken as a whole, lacks serious literary, artistic, political, or scientific value.

That third prong is crucial. Unlike the "utterly without redeeming social value" standard, it doesn't require the work to be completely worthless. It asks whether the work has "serious" value—and that judgment is made not by local community standards but by "reasonable persons" across the country. A work might offend local sensibilities in one jurisdiction while still being protected because a reasonable person anywhere could recognize its artistic merit.

The Miller test is more workable than what came before, but it remains fuzzy at the edges. "Serious" artistic value is still a judgment call. "Patently offensive" remains in the eye of the beholder. And "community standards" still vary from place to place, creating the strange situation where the same material might be obscene in one county and protected speech in the next.

The Deeper Problem: Recognition Without Definition

Why does any of this matter beyond the narrow world of obscenity law? Because Stewart's confession—"I know it when I see it"—points to something profound about human cognition.

We constantly recognize things we cannot define. Think about how you identify a friend's face in a crowd. You do it instantly and effortlessly, but could you describe their face precisely enough for a stranger to pick them out? Probably not. You know the face when you see it, but that knowledge resists translation into words.

Philosophers call this "tacit knowledge"—the kind of understanding that can be demonstrated but not articulated. A master potter knows when the clay feels right, but might struggle to explain the exact texture, temperature, and moisture level that signals readiness. A chess grandmaster sees a winning position without consciously calculating every possible move. An experienced doctor recognizes certain conditions almost immediately, through pattern recognition that outpaces explicit reasoning.

This is related to what the philosopher Ludwig Wittgenstein called "family resemblance." Some categories, Wittgenstein argued, cannot be defined by necessary and sufficient conditions. Consider the concept of "games." What feature do chess, football, solitaire, and ring-around-the-rosie all share that makes them games? Competition? Some games are solitary. Rules? Some games have no fixed rules. Fun? Some games are miserable. There is no single common thread—only a web of overlapping similarities, like the resemblances among family members.

Obscenity might be such a category. Perhaps there is no set of necessary and sufficient conditions that captures exactly what makes something obscene. Perhaps we can only recognize it through family resemblance—through accumulated experience with clear cases that allows us to judge ambiguous ones.

The Dangers of "I Know It When I See It"

But here is the problem: when legal standards depend on intuitive recognition rather than clear definition, they invite arbitrariness. My intuitions might differ from yours. What I recognize as obscene, you might recognize as art. And without articulated criteria, there is no way to resolve our disagreement through reasoned argument.

This is why some legal scholars criticized Stewart's famous phrase as "individualistic arbitrariness" dressed up as wisdom. The rule of law is supposed to be predictable. People should be able to know, in advance, whether their conduct is legal or illegal. But if the test is "whatever the judge recognizes as obscene," then the law becomes as variable as the judges who apply it.

Critics also noted a deeper logical problem. If Stewart truly couldn't articulate what made something obscene, how could he be confident in his judgment? Intuitive recognition, without the ability to explain the underlying criteria, might simply reflect unconscious bias. Perhaps Stewart's confident "I know it when I see it" was really just "I find this distasteful" or "this makes me uncomfortable"—subjective reactions masquerading as objective perception.

The "Duck Test" and Its Cousins

Stewart's phrase has a long lineage of similar reasoning. The "duck test" holds that if something looks like a duck, swims like a duck, and quacks like a duck, then it probably is a duck. This is a form of abductive reasoning—inferring the best explanation from observable evidence.

The duck test works well for ducks. Ducks have clear, stable, observable properties. But obscenity is not a natural kind like ducks. It is a legal category that humans constructed, and its boundaries depend on contested value judgments. Saying you "know obscenity when you see it" is less like recognizing a duck and more like recognizing "art" or "beauty"—categories where reasonable people perpetually disagree.

Case-based reasoning offers another model. Lawyers and ethicists often argue by analogy: this case resembles that previous case in relevant ways, so it should be decided similarly. Over time, a body of precedent builds up that guides future decisions. You might not be able to define obscenity in the abstract, but you can point to clear examples and ask whether new cases sufficiently resemble them.

This approach has its own problems. Which similarities are "relevant"? A new case always differs from previous ones in some ways and resembles them in others. Without some theory of which features matter, case-based reasoning can become as arbitrary as pure intuition.

A Mathematician's Version

The mathematician André Weil, one of the twentieth century's most influential number theorists, offered a similar confession about his own field. Paraphrasing the poet A. E. Housman, who had famously declined to define poetry ("I could no more define poetry than a terrier can define a rat, but I think we both recognize the object by the symptoms it provokes in us"), Weil suggested that number theory resisted formal definition but was recognizable nonetheless.

This is telling. Even in mathematics—that temple of precision and rigor—experts sometimes appeal to intuitive recognition. Number theory is not a natural category waiting to be discovered but a human enterprise shaped by historical accident and intellectual tradition. Its boundaries are fuzzy. Experts agree on clear cases but might disagree about whether some novel line of research truly counts as number theory or belongs to some adjacent field.

If even mathematics admits such imprecision, perhaps we should not be surprised that legal categories like obscenity resist clean definition.

What Stewart Wished He Had Said

Potter Stewart spent the rest of his life mildly regretting his famous phrase. In 1981, he reflected ruefully that his tombstone would probably feature those six words, when he would rather be remembered for the "solid words" he had written elsewhere.

This regret is poignant. Stewart had served with distinction on the Supreme Court for decades. He had written important opinions on criminal procedure, free speech, and separation of powers. He had helped shape American constitutional law in ways that affected millions of lives. But none of that could compete with one off-the-cuff admission of definitional failure.

Perhaps the phrase endured precisely because it captured something true—not just about obscenity, but about the limits of language and law. We want the law to be clear and predictable. We want legal categories to have crisp boundaries. But the world keeps presenting us with hard cases that fall into gray zones, and sometimes the most honest thing a judge can do is admit that he is operating on intuition rather than principle.

Stewart's candor was praised by some as "realistic and gallant." He could have hidden behind elaborate-sounding legal doctrines that concealed rather than revealed the underlying judgment call. Instead, he said the quiet part loud: at the end of the day, I am just a person looking at this material and forming an impression.

The Ongoing Search for Clarity

The legal system has never fully escaped the problem Stewart identified. The Miller test is more workable than "I know it when I see it," but it still requires judges and juries to make inherently subjective judgments about community standards, patent offensiveness, and serious value.

Meanwhile, the phrase has escaped law entirely and entered common speech. People invoke it whenever they want to claim recognition without definition—when they know that something is kitsch, or that an argument is sophistry, or that a situation is unfair, but struggle to articulate precisely why. The phrase has become shorthand for the gap between perception and language, between knowing and explaining.

This is Stewart's strange legacy. He wanted to be remembered for his careful legal reasoning. Instead, he is remembered for the moment when reasoning ran out—for his admission that some questions might not have articulable answers. In trying to explain what he could not define, he defined something far more universal: the experience of certain knowledge that eludes certain words.