“I saw your ghost strangle me in my sleep.” Try building a defense against that.
You could have twenty neighbors ready to swear you'd been home in bed all night, and it wouldn't matter. The Salem court accepted spectral evidence: sworn testimony that your spirit, apart from your body, had slipped out to torment the witness while you slept undisturbed. That was what made it dangerous — there was no alibi that could reach a spirit acting independently of the body, so the accusation itself became impossible to answer. Presence was never the question. Absence was no defense.
Puritan theology made the doctrine airtight. Ministers held that Satan could not borrow the shape of an innocent person without that person's consent. Appear in someone's affliction, and you had granted the Devil permission to use your image — that was standard theology, not some fringe reading of it, which meant no one on the bench considered the logic remarkable. The accusation and the proof arrived as the same event.
The result was evidence that couldn't be tested from either direction — unfalsifiable, in the modern legal sense. Modern courts require evidence that could, in principle, be challenged or disproven; spectral evidence offered no such foothold. There was no cross-examining a vision, no producing a witness to the witness's inner experience. The court was, functionally, taking dictation from an accuser's nightmares.
Bridget Bishop was the first person the court sent to the gallows, on June 10, 1692, and her case shows how little else the mechanism required. Witnesses described visions of her specter tormenting them at night; separately, neighbors offered decades-old gossip about her unconventional dress and a tavern she'd once kept. None of it was a crime on its own. Combined with spectral testimony, it was enough.
The practice didn't go unchallenged even at the time. Cotton Mather's own father, Increase Mather, argued in his 1692 pamphlet Cases of Conscience Concerning Evil Spirits that it was better for ten suspected witches to escape than for one innocent person to be condemned on such grounds. The argument helped tip the scales: Governor Phips formally barred spectral evidence from the court in October 1692. The difference showed up almost immediately — once the reorganized court stopped admitting it, most of the remaining cases ended in acquittal.
By then, nineteen people had already been hanged on exactly this kind of testimony.
The same evidentiary problem resurfaced three centuries later, in a very different courtroom. Recovered-memory testimony — a witness recalling, often during therapy, abuse they say they'd previously repressed — runs into the identical structural wall: there is no way to independently verify a subjective internal experience after the fact. Under the Daubert standard, U.S. courts have generally excluded recovered-memory testimony without outside corroboration, for close to the same reason Governor Phips gave up on spectral evidence — a court can cross-examine a person, but not a memory.
Unfalsifiable accusations remain popular. You'll notice the format survived the century.