Philology: The Study of Language and Literature
Since the Humanist movement was based on the translation and study of classical texts, an important component was the study of language. The goal was to recover the pure form of Latin and in turn to restore classical texts to their pristine form (since they had been translated into other languages, especially Arabic in Constantinople, before being translated back into Latin.)
For instance, Lorenza Valla, an Italian humanist, proved that the Donation of Constantine (the document giving control over the city of Rome to the pope) could not have been written in the 5th century, as thought, because it used words that did not exist in the fifth century.