Sebastián Izquierdo SJ (29 January 1601 – 20 February 1681) was a Spanish philosopher and Jesuit, considered a pioneer in the fields of combinatorics and mathematical logic.

The environment at these colleges was brimming with renewed interest in the work of the Catalonian philosopher Ramon Llull emphasizing theoretical mathematics, combinatorics, and methodology of science.

[4] In 1659, he published in Lyon his monumental philosophical work Pharus scientiarum (The Lighthouse of Sciences), which was widely disseminated throughout Europe.

[7] The German Jesuit Athanasius Kircher, influenced by the Pharus scientiarum, wrote his immense Ars magna sciendi an attempt to make the Lullian Ars a "science of science" suitable for the preparation of an encyclopedia of all human knowledge.

[8] Historians of mathematics remember Izquierdo especially in connection with combinatorics, to which he devoted Disputation 29 (De Combinatione).