MerjaKytö, MatsRydén & ErikSmitterberg(eds.). Nineteenth-century English: Stability and change. Cambridge: Cambridge University Press, 2006. xix + 295 pp. ISBN 13 978-0-521-86106-9
Arnaud, René. 1983. On the Progress of the progressive in the private correspondence of famous British people (1800–1880). In Sven Jacobson (ed.), Papers from the second Scandinavian symposium on syntactic variation (Stockholm Studies in English, 571), 83–94. Stockholm: Stockholm: Almqvist and Wiksell.
Huddleston, Rodney, and Geoffrey K. Pullum. 2002. The Cambridge grammar of the English language. Cambridge: Cambridge University Press.