The most popular and influential work of St. Thomas Aquinas is undoubtedly the Summa Theologica (Summary of Theology). Written between 1265 and 1274, this monumental masterpiece was intended as an instructional guide for theology students but became the cornerstone of Catholic philosophy. It is most famous for the "Five Ways" (Quinque viae), five logical arguments posited to prove the existence of God using reason. Interestingly, Aquinas left the work unfinished; following a profound mystical experience near the end of his life, he famously declared that all he had written seemed "like straw" compared to what had been revealed to him. Beyond the Summa, he is well-known for the Summa contra Gentiles and the hymn Pange Lingua, which is still sung in Catholic liturgies today during the feast of Corpus Christi.