Palmer, F. R. (1990). Modality and the English modals. Longman.
Lua i Stíl Chicago (17ú heag.)Palmer, Frank Robert. Modality and the English Modals. London: Longman, 1990.
Lua MLA (9ú heag.)Palmer, Frank Robert. Modality and the English Modals. Longman, 1990.
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