Rule 1: 1. Natural gender
Nouns for people and animals are masculine when they name a male and feminine when they name a female. Many such nouns come in pairs, the feminine being formed from the masculine by adding ة: طَبِيبٌ doctor (m.), طَبِيبَةٌ doctor (f.); مُعَلِّمٌ, مُعَلِّمَةٌ teacher. Others are different words: أَبٌ and أُمٌّ, أَخٌ and أُخْتٌ, اِبْنٌ and بِنْتٌ.
اَلطَّبِيبُ طَيِّبٌ وَالطَّبِيبَةُ طَيِّبَةٌ.
aṭ-ṭabību ṭayyibun wa-ṭ-ṭabībatu ṭayyibatun
The doctor (m.) is kind and the doctor (f.) is kind.
اِبْنٌ صَغِيرٌ وَبِنْتٌ صَغِيرَةٌ.
ibnun ṣaghīrun wa-bintun ṣaghīratun
A small son and a small daughter.
أَخِي قَوِيٌّ وَأُخْتِي قَوِيَّةٌ.
akhī qawiyyun wa-ukhtī qawiyyatun
My brother is strong and my sister is strong.
اَلْمُمَرِّضَةُ فِي غُرْفَةِ الْمَرِيضِ.
al-mumarriḍatu fī ghurfati-l-marīḍi
The nurse is in the patient's room.
أُمُّ الْوَلَدِ مُعَلِّمَةٌ.
ummu-l-waladi muʿallimatun
The boy's mother is a teacher.