Thomas Ady (fl. 17th century) was an English physician and humanist who was the author of two sceptical books on witchcraft and witch-hunting.
His first and best known work, A Candle in the Dark: Or, A Treatise Concerning the Nature of Witches & Witchcraft,[1] was used unsuccessfully by George Burroughs, formerly the Puritan minister of the parish, in his defense during the Salem witch trials.[2][3] Ady's second publication, published in 1661, was a reprint of his first, with a new title, A Perfect Discovery of Witches. The work could have been re-named in honour of Reginald Scot's Discoverie of Witchcraft, the first book of its kind in the English language. But pamphlets about cases of witchcraft tended to use 'Discovery' in their titles (The most strange and admirable discouerie of the three witches of Warboys, The vvonderfull discouerie of witches in the countie of Lancaster, etc.). Ady's point is that he discovers what 'witches' really are, despite all the accusations: innocent. His third publication was The Doctrine of Devils proved to be the grand apostacy of these later times. An essay tending to rectifie those undue notions and apprehensions men have about daemons and evil spirits (1676).