In Arabic, there is something known as sun and moon letters. Usually, the ل or lām is pronounced when ال is attached to the word. It creates the definite article, which is the equivalent of “the” in English. So you would write الكتاب which means “the book” or الرجل (definite nouns) which means “the man” instead of “كتاب” and “رجل” (indefinite nouns) which mean “book” and “man.” 

But there’s a key difference in how these words are pronounced. The ل is pronounced in the word “الكتاب” while the ل is not pronounced in the word “الرجل.” This is because of what’s known as sun and moon letters. 

In short, when a word begins with a moon letter, the ل is pronounced, but when a word begins with a sun letter, the ل is not pronounced. 

You can find a list of sun letters below. Every letter that isn’t a moon letter is a sun letter.  

Sun Letters

ت

ث

د

ذ

ر

ز

س

ش

ص

ض

ط

ظ

ل

ن