Thomas Erastus (September 7, 1524 - December 31, 1583), German-Swiss theologian, whose surname was Liber, Lieber, or Liebler, was born of poor parents, probably at Baden, canton of Aargau, Switzerland.

In 1540 he was studying theology at Basel. The plague of 1544 drove him to Bologna and thence to Padua as student of philosophy and medicine. In 1553 he became physician to the count of Henneberg, Saxe-Meiningen, and in 1558 held the same post with the elector-palatine, Otto Heinrich, being at the same time professor of medicine at Heidelberg. His patron's successor, Frederick III, made him (1559) a privy councillor and member of the church consistory.

In theology he followed Zwingli, and at the sacramentarian conferences of Heidelberg (1560) and Maulbronn (1564) he advocated by voice and pen the Zwinglian doctrine of the Lord's Supper, replying (1565) to the counter arguments of the Lutheran Johann Marbach, of Strassburg. He ineffectually resisted the efforts of the Calvinists, led by Caspar Olevianus, to introduce the Presbyterian polity and discipline, which were established at Heidelberg in 1570, on the Genevan model.

One of the first acts of the new church system was to excommunicate Erastus on a charge of Socinianism, founded on his correspondence with Transylvania. The ban was not removed till 1575, Erastus declaring his firm adhesion to the doctrine of the Trinity. His position, however, was uncomfortable, and in 1580 he returned to Basel, where in 1583 he was made professor of ethics.

He published several pieces bearing on medicine, astrology and alchemy, and attacking the system of Paracelsus. His name is permanently associated with a posthumous publication, written in 1568. Its immediate occasion was the disputation at Heidelberg (1568) for the doctorate of theology by George Wither or Withers, an English Puritan (subsequently archdeacon of Colchester), silenced (1565) at Bury St Edmunds by Archbishop Parker.

Withers had proposed a disputation against vestments, which the university would not allow; his thesis affirming the excommunicating power of the presbytery was sustained. Hence the treatise of Erastus. It was published (1589) by Giacomo Castelvetri, who had married his widow, with the title Explicatio gravissimae quaestionis utrum excommunicatio, quatenus religionem intelligentes et amplexantes, a sacramentorum usu, pro pier admissum facinus arcet, mandato natur divino, an excogitala sit ab hominibus. The work bears the imprint Pesclavii (i.e. Poschiavo in the Grisons) but was printed by John Wolfe in London, where Castelvetri was staying; the name of the alleged printer is an anagram of "Jacobum Castelvetrum." In the Stationers' Register (June 20, 1589) the printing is said to have been allowed by Archbishop Whitgift.

It consists of seventy-five Theses, followed by a Confirmatio in six books, and an appendix of letters to Erastus by Bullinger and Gualther, showing that his Theses, written in 1568, had been circulated in manuscript. An English translation of the Theses, with brief life of Erastus (based on Melchior Adam's account), was issued in 1659, entitled The Nullity of Church Censures; it was reprinted as A Treatise of Excommunication (1682), and, as revised by Robert Lee, D.D., in 1844.

The aim of the work is to show, on Scriptural grounds, that sins of professing Christians are to be punished by civil authority, and not by withholding of sacraments on the part of the clergy. In the Westminster Assembly a party holding this view included Selden, Lightfoot, Coleman and Whitelocke, whose speech (1645) is appended to Lee's version of the Theses; but the opposite view, after much controversy, was carried, Lightfoot alone dissenting. The consequent chapter of the Westminster Confession ("Of Church Censures") was, however, not ratified by the English parliament. Erastianism, as a by-word, is used to denote the doctrine of the supremacy of the state in ecclesiastical causes; but the problem of the relations between church and state is one on which Erastus nowhere enters.

What is known as Erastianism would be better connected with the name of Grotius. The only direct reply made to the Explicatio was the Tractatus de vera excommunicatione (1590) by Theodore Beza, who found himself rather savagely attacked in the Confirmatio thesium; e.g. "Apostolum et Mosen adeoque Deum ipsum audes corrigere."

See A Bonnard, Thomas Eraste et la discipline ecclésiastique (1894); Gass, in Allgemeine deutsche Biog. (1877); GV Lechler and R Sthelin, in A Hauck's Realencykiop. für prot. Theol. u. Kirche (1898).

This article incorporates text from the public domain 1911 Encyclopædia Britannica.