The humanists' close study of Latin literary texts soon enabled them to discern historical differences in the writing styles of different periods. By analogy with what they saw as decline of Latin, they applied the principle of ad fontes, or back to the sources, across broad areas of learning, seeking out manuscripts of Patristic literature as well as pagan authors. In 1439, while employed in Naples at the court of Alfonso V of Aragon (at the time engaged in a dispute with the Papal States) the humanist Lorenzo Valla used stylistic textual analysis, now called philology, to prove that the Donation of Constantine, which purported to confer temporal powers on the Pope of Rome, was an 8th-century forgery. For the next 70 years, however, neither Valla nor any of his contemporaries thought to apply the techniques of philology to other controversial manuscripts in this way. Instead, after the fall of the Byzantine Empire to the Turks in 1453, which brought a flood of Greek Orthodox refugees to Italy, humanist scholars increasingly turned to the study of Neoplatonism and Hermeticism, hoping to bridge the differences between the Greek and Roman Churches, and even between Christianity itself and the non-Christian world. The refugees brought with them Greek manuscripts, not only of Plato and Aristotle, but also of the Christian Gospels, previously unavailable in the Latin West.

How were humanist able to identify the development of humanist thought?