The Ninth Amendment: The Rights We Never Wrote Down.

“The enumeration in the Constitution, of certain rights, shall not be construed to deny or disparage others retained by the people.” — U.S. Const. amend. IX

Most of the Bill of Rights tells the government what it cannot do. The Ninth Amendment does something stranger: it protects rights the Constitution never actually names. Think of it as a stand-in for everything the Framers knew they had left off the list — their way of saying, in writing, that no list of freedoms could ever cover them all.

That bit of modesty is itself a psychological insight. The same Framers who built checks and balances to guard against human mistakes also knew the limits of their own imagination. They could not predict every freedom a future citizen might need, so they wrote a rule to cover the rights they hadn’t thought of yet. Some of them even worried that listing rights at all was risky: people might read the list as complete and treat anything left off as fair game. The Ninth Amendment was their answer to that worry — a reminder that just because a right isn’t written down doesn’t mean you don’t have it.

For most of American history, that reminder was ignored. In a 1967 article in the Marquette Law Review, Luis Kutner called it “the neglected Ninth Amendment,” because courts and scholars never quite knew what to do with a right that doesn’t spell out what it protects. One famous law professor, John Hart Ely, joked that in serious legal circles, bringing up the Ninth Amendment was “a surefire way to get a laugh.” It’s worth asking why a whole legal culture would look past something so plainly written. We tend to focus on what’s concrete and spelled out; an open-ended promise gives the mind nothing to hold onto. The very thing that makes the Ninth Amendment valuable — that it refuses to be a fixed list — is exactly what made it easy to forget.

Randy Barnett’s 2006 Texas Law Review article, pointedly titled “The Ninth Amendment: It Means What It Says,” argues that ignoring it was a mistake. After working through the historical record, Barnett concludes that the Amendment means today exactly what it appears to say: the basic rights people had before any government existed — and kept afterward — deserve the same respect as the rights actually listed in the Bill of Rights. The Ninth, in his view, isn’t a footnote but “a meaningful check on federal power and a significant guarantee of individual liberty.”

So why should a legal psychology lab care about a clause about unwritten rights? Because the questions it raises are really questions about the mind — and they’re no longer hypothetical. In a 2025 essay in the Indiana Law Journal, “Ninth Amendment Neurorights,” Joseph Tomain makes what he calls the “relatively easy case” that the Ninth protects two freedoms the Framers never had to name, because in their day no one could threaten them: the freedom to think your own thoughts and the privacy of your own mind.

Those freedoms can be threatened now. Tomain lays out what brain technology can already do. Researchers have used brain scans — no surgery required — to turn people’s unspoken thoughts into sentences. Computer programs have predicted someone’s political views, and even their sexual orientation, just from the structure and activity of their brain. More than a decade ago, scientists planted a false memory in the brain of a mouse. Companies have even tested ways to slip a brand into your dreams as you drift off to sleep. For centuries, the home stood as the law’s symbol of a truly private space. The Ninth Amendment, Tomain argues, should protect the one place even more private than the home: the mind itself.

This is where psychology and the law meet most directly. Freedom of thought is the foundation under every other right in the Bill of Rights — the freedom to speak, to believe, to weigh evidence as a juror, to stay silent as a defendant. If our private thoughts can be read, predicted, or rewritten, all the rights built on top of them start to crumble. Tomain adds a warning that should ring true for anyone who studies how people actually make decisions: the biggest threat may not be the government at all, but companies, which face fewer legal limits and a strong financial reason to reach inside our heads — what scholars call the forum internum, the inner space of the mind.

The Framers wrote the Ninth Amendment because they knew their list of rights was incomplete. They could never have pictured a brain scan or an ad planted in a dream. But they wrote the clause precisely for the rights they couldn’t see coming, and in doing so they left a door open for us. Two and a half centuries later, the freedom to think your own thoughts — unread and unchanged — may turn out to be exactly the kind of unlisted right they were trying to protect. The Ninth Amendment reminds us that some of our most basic protections were never written down. Not because they didn’t matter, but because, for a long time, no one imagined they would ever need defending.