Some current research that has investigated the diglossia phenomena in the Arabic language--a phenomenon in which two spoken forms are used by one community, indicates that traditional Arabic grammarians had some biases when they crafted the Arabic grammar books. Sibawah, a Basran Arabic grammarian philologist, is an example of such biases (1), wo had standardized Arabic grammar based on a particular variety while neglecting other spoken verities(2). Such a bias has created an idealized and standard language which is not compatible with Arabic spoken varieties during Sibawah’s time . In this paper, I discuss one Arabic sound--glottal sound, that was standardized by either adding it to Arabic lexicon or by tensing some lexical items that have a light glottal sound. For instance, some lexical items such as (fās, dīb, mūmın) were standardized with a glottal sound as (fāʾs, dīʾb, muʾmın). Some Arabic philologists have considered this sound a standard form since it was an easy process of marking the written forms with some diacritics (3), i.e. vocalic materials. This paper attempts to answer the following questions: (1) To what extent can we, linguists, consider these sound changes provided by some traditional philologists a mistake or misjudgment? (2) To what extent can we reconstruct the addition of the glottal sound to consider the original sounds as the standard? In this paper, I analyze the glottal sound change by comparing some data extracted from four Arabic grammar documents authored by Sibawih, Ibn Jinni, Ibn Khaldun, Ibn Madaʾ(4)The conclusion is that old Arab communities during 8th A.D or even before it were uttering the glottal sound when there are ambiguities with other lexical items. This result leads me to another future research work which is to what extent we can collapse this glottal sound in some Arabic curricula since it is a troublesome issue for Arabic native learners. Reference: 1 Ar.Radd Ala Annuhat, Ibn Madaā al-Qurtubi 2 Al Etqān Fī Ūlūm Al.Qurān, Al.Sūyūtī 3 Al.Kitāb, Sibawīh, and Al.Nahu Al.Jadeed, Abdulmutaāli Al.Saēdī 4 Al.Kitāb, Sibawīh. Al.Khasāys, Ibn Jinni. Al.Muqaddimah, Ibn Khaldoun. Ar.Radd Ala Annuhat, Ibn Madaā al-Qurtubi