LessonsRefining Qualities and the Detailed Rules of Lam and RaQuiz

An original kasrah before still ra usually makes it light. An important exception occurs when the next letter, within the same word, is one of the letters of istiʿla: خ، ص، ض، غ، ط، ق، ظ (remembered in «خُصَّ ضَغْطٍ قِظْ»).

«قِرْطَاسٍ» — kasrah precedes the still ra, but the following ط makes ra heavy.
«مِرْصَادًا» — the following ص similarly calls for heavy ra.

Both aspects matter: examine the preceding kasrah, and confirm that the emphatic letter follows the ra in that same word. A heavy consonant elsewhere cannot simply be substituted into this rule.

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Third exception: an emphatic letter after ra

Refining Qualities and the Detailed Rules of Lam and Ra

An original kasrah before still ra usually makes it light. An important exception occurs when the next letter, within the same word, is one of the letters of istiʿla: خ، ص، ض، غ، ط، ق، ظ (remembered in «خُصَّ ضَغْطٍ قِظْ»).

«قِرْطَاسٍ» — kasrah precedes the still ra, but the following ط makes ra heavy.
«مِرْصَادًا» — the following ص similarly calls for heavy ra.

Both aspects matter: examine the preceding kasrah, and confirm that the emphatic letter follows the ra in that same word. A heavy consonant elsewhere cannot simply be substituted into this rule.