The Theravāda tradition bases itself on the Pāli Canon, considers itself to be the more orthodox form of Buddhism and tends to be more conservative in doctrine and monastic discipline. The Pāli Canon is the only complete Buddhist canon surviving in an ancient Indian language. This language, Pāli, serves as the school's sacred language and lingua franca. Besides the Pāli Canon, Theravāda scholastics also often rely on a post-canonical Pāli literature which comments on and interprets the Pāli Canon. These later works such as the "Visuddhimagga", a doctrinal "summa" written in the fifth century by the exegete Buddhaghosa also remain influential today.