٣٢- Firth, J.R: Papers in Linguistics, "Oxford University Press, ١٩٦٧".
٣٣- Gairdner, W.H.T: The Phonetics of Arabic, "Oxford University Press,١٩٢٥".
٣٤- Heffner, R.M.S: General Phonetics "The University of Wisconsim Press ١٩٦٠".
٣٥- Hass, W: Zero in linguisitcs "Studies in Linguistic analysis, special vol. of the Philological Society. ١٩٥٧, pp. ٣٣-٥٣".
٣٦- Robins, R.H: General Linguistics: An Introductory Suvey Longmans, Green & Co. Ltd. ١٩٦٤".
٣٧- Wright, W: A Grammar of the Arabic Language, translated from the German of Caspari, "third ed., Cambridge University Press, ١٩٥١".