Ralph Cudworth (1617 – 26 June 1688) was an English philosopher, the leader of the Cambridge Platonists.
Somerset, he was educated at Emmanuel College, Cambridge, gaining his MA and becoming a Fellow of Emmanuel in 1639. In 1645, he became master of Clare Hall and professor of Hebrew. In 1654, he transferred to Christ's College, Cambridge, and was master there until his death. His great work, entitled The True Intellectual System of the Universe, was published in 1678. He was a leading opponent of Thomas Hobbes.
His father Dr. Ralph Cudworth, a Fellow of Emmanuel College, Cambridge, was presented to the rectory of Aller, Somerset by his college, which held the advowson, in c.1609 or 1610. On 18 June 1611 at Southwark he married Mary Machell of Hackney (who had been a nurse to Prince Henry the son of James I) and their children were christened at Aller over the following decade.
Dr. Cudworth died in 1624 when young Ralph was about 7, and his mother then married John Stoughton, who succeeded Dr. Cudworth as rector of Aller until 1632 and gave the boy a good home education. Ralph was sent to his father's college, was elected Fellow in 1639 and became a successful tutor. In 1642 he published A Discourse concerning the true Notion of the Lord's Supper and a tract entitled The Union of Christ and the Church. In 1645 he was appointed master of Clare Hall and the same year was elected Regius professor of Hebrew. He was now recognized as a leader among the remarkable group known as the Cambridge Platonists. The whole party was more or less in sympathy with the Commonwealth, and Cudworth was consulted by John Thurloe, Cromwell's secretary to the council of state, in regard to university and government appointments.
In 1650 he was presented to the college living of North Cadbury, Somerset. From the diary of his friend John Worthington we learn that Cudworth was nearly compelled, through poverty, to leave the university, but in 1654 he was elected master of Christ's College, whereupon he married. In 1662 he was presented to the rectory of Ashwell, Herts. In 1665 he almost quarrelled with his fellow-Platonist, Henry More, because the latter had written an ethical work which Cudworth feared would interfere with his own long-contemplated treatise on the same subject. To avoid clashing, More brought out his book, the Enchiridion ethicum, in Latin; Cudworth's never appeared. Cudworth was installed prebendary of Gloucester in 1678. He died on 26 June 1688, and was buried in the chapel of Christ's. His only surviving child, Damaris, a devout and talented woman, became the second wife of Sir Francis Masham. The Lady Masham was distinguished as the friend of John Locke and exchanged letters with Gottfried Leibniz.