Metslang (2017), p.302. Metslang, Helle (2017). "10. Can a language be forced? The case of Estonian". In Van Olmen, Daniel; Cuyckens, Hubert; Ghesquière, Lobke (eds.). Aspects of Grammaticalization: (Inter)Subjectification and Directionality. Trends in Linguistics. Studies and Monographs. Vol.305. De Gruyter Mouton. pp.281–310. doi:10.1515/9783110492347-011. ISBN9783110489699. ISSN1861-4302.
Metslang (2017), p.302. Metslang, Helle (2017). "10. Can a language be forced? The case of Estonian". In Van Olmen, Daniel; Cuyckens, Hubert; Ghesquière, Lobke (eds.). Aspects of Grammaticalization: (Inter)Subjectification and Directionality. Trends in Linguistics. Studies and Monographs. Vol.305. De Gruyter Mouton. pp.281–310. doi:10.1515/9783110492347-011. ISBN9783110489699. ISSN1861-4302.