Cautio Criminalis, or a Book on Witch Trials

Published in Germany in 1631, Friedrich Spee's Cautio Criminalis is a treatise that argued (at the time anonymously) against witchcraft prosecutions. Many of Spee's points today may seem obvious — we live in a more scientifically-inclined age that views witch trials as extreme and even a bit ridiculous — but he is persuasive in his attack on the inhumane and unfair nature of the investigations. Spee also makes broader arguments agains the veracity of confessions obtained under duress:

Torture has the power to create witches where none exist... The tortured say yes to everything, and because they do not dare to withdraw, they must seal everything with death.

If both confession and silence are taken as signals of guilt then everyone is guilty. Truth evaporates.

Spee's radicalism has some limits — he didn't deny that witches and sorcerers exist — but this is a nonetheless a good early example of skepticism in the face of a fairly popular movement.