Charles Leslie (nonjuror)
He was the son of John Leslie (1571-1671), bishop of Raphoe and afterwards of Clogher, born in July 1650 in Dublin, and educated at Enniskillen school and Trinity College, Dublin. Going to England he read law for a time, but soon turned his attention to theology, and took orders in 1680. In 1687 he became chancellor of the cathedral of Connor and a justice of the peace.
He began a long career of public controversy by responding in public disputation at Monaghan to the challenge of the Roman Catholic bishop of Clogher. Although a vigorous opponent of Roman Catholicism, Leslie was a firm supporter of the Stuart dynasty, and, having declined at the Glorious Revolution to take the oath to William and Mary, he was on this account deprived of his benefice.
In 1689 the growing troubles in Ireland induced him to withdraw to England, where he employed himself for the next twenty years in writing various controversial pamphlets in favor of the nonjuring cause, and in numerous polemics against the Quakers, Jews, Socinians and Roman Catholics, and especially in that against the Deists with which his name is now most commonly associated. He had the keenest scent for every form of heresy and was especially zealous in his defence of the sacraments. In 1704 Leslie started his weekly periodical The Observator (1704-9), changing its name to The Rehearsal of Observator in 1705 and then to The Rehearsal. In this work he expounded his Jacobite political principles and attacked the Whiggish and Dissenting views of John Tutchin's Observator (founded 1702) and Daniel Defoe's Review (1704–13).
A warrant having been issued against him in 1710 for his pamphlet The Good Old Cause, or Lying in Truth, he resolved to quit England and to accept an offer made by the Pretender (with whom he had previously been in frequent correspondence) that he should reside with him at Bar-le-Duc. After the failure of the Stuart cause in 1715, Leslie accompanied his patron into Italy, where he remained until 1721, in which year, having found his sojourn amongst Roman Catholics extremely unpleasant, he sought and obtained permission to return to his native country. He died at Glaslough, Monaghan, on the 13 April 1722.
The Theological Works of Leslie were collected and published by himself in 2 vols folio in 1721; a later edition, slightly enlarged, appeared at Oxford in 1832 (7 vols 8vo).
An historical interest is all that now attaches to his subjects and his methods, as may be seen when the promise given in the title of his best-known work is contrasted with the actual performance. The book professes to be "A Short and Easy Method with the Deists wherein the certainty of the Christian Religion is Demonstrated by Infallible Proof from Four Rules, which are incompatible to any imposture that ever yet has been, or that can possibly be" (1697). The four rules which, according to Leslie, have only to be rigorously applied in order to establish not the probability merely but the absolute certainty of the truth of Christianity are simply these:
- that the matter of fact be such as that men's outward senses, their eyes and ears, may be judges of it
- that it be done publicly, in the face of the world
- that not only public monuments be kept up in memory of it, but some outward actions be performed
- that such monuments and such actions or observances be instituted and do commence from the time that the matter of fact was done.
Other publications of Leslie are:
- The Snake in the Grass (1696), against the Quakers 
- A Short Method with the Jews (1689)
- Galhienus Redivivus (an attack on William III, 1695)
- The Socinian Controversy Discussed (1697)
- A discourse; shewing, who they are that are now qualify'd to administer baptism and the Lord's-Supper (1698)
- The True Notion of the Catholic Church (1703)
- The Case Stated between the Church of Rome and the Church of England (1713)
- Leslie Genealogy
- Full title: The snake in the grass: or, Satan transform'd into an angel of light, discovering the deep and unsuspected subtilty which is couched under the pretended simplicity, of many of the principal leaders of those people call'd Quakers. - London : printed for Charles Brome, at the Gun at the west-end of St. Paul's
- This article incorporates text from a publication now in the public domain: Chisholm, Hugh, ed. (1911). "Leslie, Charles". Encyclopædia Britannica (11th ed.). Cambridge University Press.