Sun and moon letters

When followed by a sun letter, the /l/ of the Arabic definite article al- assimilates to the initial consonant of the following noun, resulting in a doubled consonant. For example, for "the Nile", one does not say al-Nīl, but an-Nīl.

When the Arabic definite article (الْـ) is followed by a moon letter, no assimilation takes place.

The sun letters represent the coronal consonants according to the phonology of Classical Arabic, and the moon letters represent all others. The sun and moon letters are as follows:

The sun (konsonanti xemxin) and moon (konsonanti qamrin) letters are as follows:

If a word starts with any of the moon letters, the definite article il- stays the same and does not assimilate, while with the sun letters it assimilates accordingly to to: iċ-, id-, in-, ir-, is-, it-, ix-, iż-, iz-. It is also worth mentioning that words starting with vowels, and the letters għ, and h get the definite article l- (minus the initial i). When the definite article comes exactly after a word ending in a vowel, the initial <i> of the article always drops, as in "dak ir-raġel ra r-raġel" (that man saw the man). When a word starts with two consonants, the definite article used is l-, but an i is attached at the beginning of the word: skola > l-iskola and Żvezja > l-Iżvezja.[2]

In the written language, the ال al- is retained regardless of how it is pronounced.[1] When full diacritics are used, assimilation may be expressed by putting a shaddah on the consonant after the lām. Non-assimilation may be expressed by placing a sukūn over the lām.

Most modern-written Arabic names (including personal names and geographical Arabic names) do not follow the consonant assimilation rule or the shaddah when latinized in Latin-spelled languages. Sometimes the sun and moon rules are not followed in casual speech.

E.g. personal name: الرَّحْمَن - Al-Rahman instead of "Ar-Raḥmān";

geographical name: الْجُمْهُورِيَّةُ التُّونِسِيَّة - Al-Jumhuriyah Al-Tunisiyah instead of "al-Jumhūrīyatu ’t-Tūnisīyah".

• Arabic phonology
• Arabic grammar