“I saw your ghost strangle me in my sleep.” Try building a defense against that.
The Salem court accepted spectral evidence — sworn testimony that the accused's spirit, separate from their physical body, had appeared to the witness and caused them harm. A defendant could produce twenty neighbors willing to swear she'd been home in bed all night, and it would change nothing. Her specter, the argument went, could still have slipped out to do the Devil's work.
This wasn't a fringe theory — it was standard Puritan theology, and that's precisely what made it so dangerous in a courtroom. The prevailing belief held that Satan could not borrow the shape of an innocent person without that person's consent. If you appeared in someone's affliction, logically, you must have granted the Devil permission to use your image. The accusation and the proof were the same event.
It also meant the evidence was unfalsifiable by design. 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.
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. His argument helped tip the scales — Governor Phips formally barred spectral evidence from the court in October 1692, and the trials collapsed within months.
By then, nineteen people had already been hanged on exactly this kind of testimony.
Unfalsifiable accusations remain popular. You'll notice the format survived the century.