Seth Ward (1617 – 6 January 1689) was an English mathematician, astronomer, and bishop.
He was born in Hertfordshire, and educated at Sidney Sussex College, Cambridge, where he graduated B.A. in 1636 and M.A. in 1640, becoming a Fellow in that year. In 1643 he was chosen university mathematical lecturer, but he was deprived of his fellowship next year for opposing the Solemn League and Covenant (with Isaac Barrow, John Barwick and Peter Gunning).
In the 1640s, he took instruction in mathematics from William Oughtred, and stayed with relations of Samuel Ward.
In 1649, he became Savilian professor of astronomy at Oxford University, and gained a high reputation by his theory of planetary motion. It was propounded in the works entitled In Ismaelis Bullialdi astro-nomiae philolaicae fundamenta inquisitio brevis (Oxford, 1653), against the cosmology of Ismael Boulliau, and Astronomia geometrica (London, 1656) on the system of Kepler. About this time he was engaged in a decades-long philosophical controversy with Thomas Hobbes: Seth Ward and John Wallis, both Savilian professors and members of the Anglican clergy, felt offended by the works of Hobbes, particularly after Leviathan was released.
A small part of the debate with John Webster launched by the Vindiciae academiarum he wrote with John Wilkins which also incorporated an attack on William Dell.