6Abraham, Werner( 1991 ) The grammaticalization of the German modal particles. In E.C. Traugott and B. Heine .(eds.), Approaches to Grammaticalization, Vol. Ⅱ, 331 -380. Amsterdam: John Benjamins Publishing Company.
7Hurtle, W. H.(1977) Already, still, and yet. Archivum Linguisticum 8,28 -45.
8Konig, Ekkehard, and Elizabeth C. Traugott(1982) Divergence and apparent convergence in the development of yet and still. Proceedings of the Eighth Annual Meeting of the Berkeley Linguistics Society, 170 -79. Berkeley, CA : Berkeley Linguistics Society.
9Michaelis, Laura A.(1996) Cross-world continuity and the polysemy of adverbial still. In G. Fauconnier and E. Sweetser .(eds.), Spaces, Worlds, and Grammar, 179 -266. Chicago: The University of Chicago Press.
10Traugott, E. C.(1995) Subjectification in grammaticalization. In D. Stein & S. Wright .(eds.), Subjectivity and Subjectivisation, 31 - 54. Cambridge : Cambridge University Press.