The article and sun letters

Arabic has one definite article, ال, written joined to its noun: كتاب (a book), الكتاب (the book). There is no word for a or an: the noun alone is indefinite.

Before a sun letter, the l of the article is silent and the next letter doubles: الشمس, النور, الرجل. Before a moon letter the l is heard: القمر, الباب, الكتاب. It is always written.

After the preposition لـ (for, to), the alif of the article drops: للطالب, not لالطالب. After و and بـ it stays: والكتاب, بالقلم.