هَذِهِ مَصَابِيحُ — These are lamps; maṣābīḥ is a nominative predicate.
أَضَأْتُ مَصَابِيحَ — I lit lamps; maṣābīḥ is an accusative object.
نَظَرْتُ إِلَى مَصَابِيحَ — I looked toward lamps; maṣābīḥ is genitive with fatḥa.
After the plural alif come ب، يْ، ح. This specific structure makes the plural a diptote.
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Diptote Causes — Ultimate Broken-Plural Patterns
هَذِهِ مَصَابِيحُ — These are lamps; maṣābīḥ is a nominative predicate.
أَضَأْتُ مَصَابِيحَ — I lit lamps; maṣābīḥ is an accusative object.
نَظَرْتُ إِلَى مَصَابِيحَ — I looked toward lamps; maṣābīḥ is genitive with fatḥa.
After the plural alif come ب، يْ، ح. This specific structure makes the plural a diptote.