Iṭbāq involves a close tongue-palate posture. The book assigns it to just four letters: ص ض ط ظ. They have a characteristic fuller quality.
Compare ص with س and ط with ت. Do not interpret iṭbāq as forcibly fixing the entire tongue against the palate. The true articulation point still matters, especially the side-of-tongue articulation of ḍād.
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Iṭbāq: the four letters
Ṣifāt al-Ḥurūf — Opposing Qualities and Strength Grades
Iṭbāq involves a close tongue-palate posture. The book assigns it to just four letters: ص ض ط ظ. They have a characteristic fuller quality.
Compare ص with س and ط with ت. Do not interpret iṭbāq as forcibly fixing the entire tongue against the palate. The true articulation point still matters, especially the side-of-tongue articulation of ḍād.