1. Helsinki Corpus of English Texts (1991) Compiled by Rissanen, Matti, Merja Kytö, Leena Kahlas-Tarkka, Matti Kilpiö, Saara Nevanlinna, Irma Taavitsainen, Terttu Nevalainen and Helena Raumolin-Brunberg. Helsinki: University of Helsinki.
2. Oxford English Dictionary, 2nd edition (1989) Edited by Simpson, John A. and Edmund Weiner. [CD-Rom]. Oxford: Oxford University Press.
3. Parsed Corpus of Early English Correspondence, parsed version (2006) Compiled by Taylor, Ann, Arja Nurmi, Anthony Warner, Susan Pintzuk and Terttu Nevalainen. Helsinki: University of Helsinki and York: University of York.
4. Conde-Silvestre, Juan C. and Javier Calle-Martín (2015) Zero that-clauses in the history of English: A historical sociolinguistic approach (1424–1681). Journal of Historical Sociolinguistics 1 (1), 57–86.
5. Fisher, John H. (1977) Chancery and the emergence of standard written English in the fifteenth century. Speculum 52 (4), 870–899.