Fifty Years of “I know it when I see it.”

On June 22, 1964, Justice Potter Stewart coined the phrase “I know it when I see it” in his concurring opinion in Jacobellis v. Ohio. Fifty years later, that expression holds the distinction of being one of the few modern legal phrases to become a regularly accepted expression among educated Americans. The half-century anniversary of Jacobellis provides a fitting opportunity to ask why “I know it when I see it” has enjoyed such popularity and what lessons that phrase and its history might hold for us today.

Jacobellis reversed the conviction of an Ohio movie theater manager for showing obscene material in the form of the French film Les Amants (The Lovers), which included a sex scene at its conclusion. The court’s 6-3 decision was highly fragmented, with six opinions in total and the plurality garnering only two votes.

Potter Stewart

In a short 144-word concurring opinion, Stewart wrote that he found it almost impossible to define obscenity precisely, which should only include “hard-core pornography.” His now famous line concluded the opinion:

 “But I know it when I see it, and the motion picture involved in this case is not that.”

At the time, the pithy phrase actually garnered little interest in the public sphere. Many newspapers chose instead to focus on another obscenity case decided that same day, Quantity of Books v. Kansas. Those journalists who did write about Jacobellis largely ignored “I know it when I see it” and chose to focus on the legal technicalities the case posed.

While it is difficult to pinpoint exactly when Stewart’s iconic expression became common, we can chart its growing popularity via Google’s Ngram search engine. Google Ngram measures the percentage of English language books that contain a phrase up to five words long. Because “I know it when I see it” is seven words, I ran the search for each five-letter segment of the phrase (“I know it when I;” “know it when I see;” “it when I see it.”). The graph clearly shows the steeply rising and still growing interest in Stewart’s phrase, starting slightly after 1964:

I know it when I see it Ngram


The Ngram search also reveals some interesting instances of similar phrases, both legal and not, pre-dating Jacobellis. Consider two examples: In an obituary for Benjamin Cardozo that ran in the Columbia, Yale and Harvard law journals in 1939, Learned Hand praised Justice Cardozo for his wisdom, writing:

“And what is wisdom — that gift of God which the great prophets of his race exalted? I do not know; like you, I know it when I see it, but I cannot tell of what it is composed.”

Woodrow Wilson used almost the same phrasing two decades earlier. Discussing German attacks on American shipping prior to U.S. entry in the First World War, Wilson said in a 1919 San Francisco speech that he had not known precisely what would count as an “intolerable” act of war against the US: “but I am,” he said, “perfectly certain I will know it when I see it.”

While Stewart might have known of these pre-Jacobellis uses of the term, especially Hand’s obituary for Cardozo, he was neither referencing them nor intending to create a widespread sensation. In 2007, YLS librarian and phrase-smith Fred Shapiro tracked down Alan Novak, Stewart’s clerk in 1964. Novak remembered the phrase emerging out of a conversation with the justice. And it was, according to Novak, Stewart who wrote the actual opinion, including the seven words.

The unintentional popularity of “I know it when I see it” should be a note of caution for legal authors in the public sphere, from jurists to commentators more generally: it is very difficult to predict in advance what will capture widespread attention among the non-legal public. This is true of other well-known legalisms, such as Oliver Wendell Holmes Jr.’s oft-cited example of a man falsely shouting fire in a crowded theater. (See Thomas Healy’s excellent book on Holmes, The Great Dissent.) On the flip side, the legal corpus is full of opinions whose authors hoped would be earthquakes but whose prose was then largely ignored.

What is it about “I know it when I see it” that is so particularly appealing? The phrase has earned both public attention and the distinction of being one of the few legalisms that has outgrown the confines of legalese: People use Potter Stewart’s language today without knowing its origin within the law. While other legal phrases, such as “for all intents and purposes,” have made similar transitions into everyday speech, they are far older, often with roots in English common law. Most have taken centuries to trickle into Anglo-American vocabulary.

(Tom Clancy fans might quibble with me, pointing to his novel Clear and Present Danger as an exception — and another example of a well-known Holmes phrase.)

In contrast, “I know it when I see it” is today popular in almost every field of study and throughout the public sphere. In the course of my own historical research, I by accident found two scholars who have used the term in attempts to define propaganda, which led me to write this post. While a full rendition of those authors who have appropriated Stewart’s phrase would be so long as to be counterproductive, it is sufficient to say the list is extensive.

In a 1996 article in the Yale Law Journal, Paul Gewirtz suggests that part of what draws us to “I know it when I see it” is it’s non-rational element. For Gewirtz, Stewart’s seven words capture the kind of intuitive, gut thinking made famous in Malcom Gladwell’s Blink.

There is much merit to Gewirtz’s point, but “I know it when I see it” further benefits from an allusion simultaneously to the rational, or more precisely, algorithmic thinking.[1] “I know it when I see it” implies that an algorithm, a test or a standard exists, but that it is difficult to articulate. When we use the phrase, we imply that we are not being arbitrary or capricious, but we are judging whatever is under judgment methodically. Unlike “taking something on a case by case basis” — another expression you hear quite frequently —  “I know it when I see it” implies a uniformity in our logic which applies to every item we are examining. In other words, we are being quite deliberate; we just don’t know how to describe our internal deliberation.

Happy birthday to Potter Stewart’s phrase. Here’s to fifty more years of knowing and seeing.


[1] Gewirtz does note that Stewart’s entire opinion as a whole, not the seven words, is highly rational.

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1 Response

  1. Joe says:

    Justice Stewart might have been sensitive to response to his usage himself since he noted shortly after the opinion in a dissenting opinion to Ginzburg v. U.S.:

    “I have referred to such material before as hard-core pornography, without trying further to define it. Jacobellis v. Ohio, 378 U. S. 184, at 378 U. S. 197 (concurring opinion). In order to prevent any possible misunderstanding, I have set out in the margin [footnote provided] a description, borrowed from the Solicitor General’s brief, of the kind of thing to which I have reference.”