Rule 1: 1. مَا of vagueness
An indefinite noun, in whatever case the sentence requires, is followed by the invariable particle مَا. The noun keeps its tanwīn and مَا adds nothing to the grammar; it only tells the listener that the speaker cannot or will not be more precise. Common phrases: يَوْمًا مَا some day, فِي مَكَانٍ مَا somewhere, شَخْصٌ مَا someone or other, لِسَبَبٍ مَا for some reason, بِشَكْلٍ مَا somehow, إِلَى حَدٍّ مَا to a certain extent, نَوْعًا مَا somewhat.
سَيُصَوِّتُ الْمَجْلِسُ عَلَى الْمَشْرُوعِ يَوْمًا مَا.
sa-yuṣawwitu l-majlisu ʿalā l-mashrūʿi yawman mā
The council will vote on the bill some day or other.
يَوْمًا accusative of time, then مَا.
اَلْحُكُومَةُ مَسْؤُولَةٌ إِلَى حَدٍّ مَا عَنْ سُوءِ الْأَحْوَالِ.
al-ḥukūmatu masʾūlatun ilā ḥaddin mā ʿan sūʾi l-aḥwāli
The government is responsible to a certain extent for the bad conditions.
Genitive after إِلَى; مَا unchanged.
اِخْتَارَتِ الْبَعْثَةُ مَوْقِعًا مَا فِي الصَّحْرَاءِ.
ikhtārati l-biʿthatu mawqiʿan mā fi ṣ-ṣaḥrāʾi
The mission chose a certain site in the desert.
اِنْسَحَبَ النَّائِبُ مِنَ الْجَلْسَةِ لِسَبَبٍ مَا.
insaḥaba n-nāʾibu mina l-jalsati li-sababin mā
The deputy withdrew from the session for some reason.
سَمِعْتُ أَنَّ شَخْصًا مَا انْتَقَدَ الْوَزِيرَ عَلَنًا.
samiʿtu anna shakhṣan mā ntaqada l-wazīra ʿalanan
I heard that someone or other criticised the minister openly.