Sebastián Izquierdo

Sebastián Izquierdo (1601 to 1681) was a Spanish Jesuit philosopher, born at Alcaraz in the Castilian province of Albacete, who is remembered in the history of mathematics as an early student of combinatorics and mathematical logic. He entered the Society of Jesus in 1623, studied at Alcalá de Henares and the Colegio Imperial de Madrid, and taught philosophy and theology at Alcalá, Murcia and Madrid, serving as rector of the colleges of Murcia and Madrid. A follower of Ramon Llull who was also influenced by Bacon's empiricism, he argued in his Pharus scientiarum (1659) for a universal science valid for all human knowledge and proposed replacing Llull's letter combinations with number combinations. Disputation 29 of that work, De Combinatione, is the first discussion of the number of k-combinations of n elements, and Leibniz quoted it in his De Arte Combinatoria. Izquierdo died in Rome in 1681.