Pakpahan, B. “The Correlation of the Meanings of Verbs Pouvoir and Devoir in French and Their Equivalent in Indonesian”. International Journal of Sciences: Basic and Applied Research (IJSBAR), vol. 32, no. 1, Mar. 2017, pp. 247-69, https://www.gssrr.org/index.php/JournalOfBasicAndApplied/article/view/6917.