Really well analyzed.
In the pursuit of academic accuracy we should not completely deny our instincts. This might be the case of "I know it when I see it."
The phrase comes from a famous opinion by Potter Stewart, a justice on the Supreme Court of the United States, in the 1964 obscenity case Jacobellis v. Ohio.
The actual quote was:
“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 I could never succeed in intelligibly doing so. But I know it when I see it.”
Stewart was explaining the difficulty of creating a precise legal definition for “hard-core pornography” or obscenity. The Court was trying to decide whether a film was legally obscene and therefore unprotected by the First Amendment.
Over time, the quote got shortened and paraphrased into versions like:
“Pornography cannot be defined, but you know it when you see it.”
“I can’t define pornography, but I know it when I see it.”
The phrase became culturally famous because it captures a broader idea: some categories are hard to define formally, yet people feel they can recognize them intuitively. It’s now used far beyond pornography law — in aesthetics, politics, AI, ethics, and everyday speech.
As an atheist, I know that this is partially hypocritical, because I'm allowing personal experience to have a lot of power in this case. The reason it's partial though, is because I'm basing the experience on a natural phenomena.