Textual criticism is a branch of textual scholarship, philology, and literary criticism that is concerned with the identification of textual variants, or different versions, of either manuscripts (mss) or of printed books. Such texts may range in dates from the earliest writing in cuneiform, impressed on clay, for example, to multiple unpublished versions of a 21st-century author's work. Historically, scribes who were paid to copy documents may have been literate, but many were simply copyists, mimicking the shapes of letters without necessarily understanding what they meant. This means that unintentional alterations were common when copying manuscripts by hand. Intentional alterations may have been made as well, for example, the censoring of printed work for political, religious or cultural reasons.