Basic Declension
- الكتابُ مفتوحٌ
- اشتريتُ الكتابَ بعشرينَ دولارا
- على الكتابِ قلمٌ ومسطرةٌ
- المعلومةُ في الكتابِ
- The book is open
- I bought the book for $20
- There are a pen and a ruler on the book
- The information is in the book
It's importance
Declension is very important in Arabic.
Take the word "book" in English. Whenever it is used it retains the same form, with the same vowels in the same places. This is different with the word الكتاب above. While most of its vowels remain the same, the final one is not fixed and is seen above to turn into all three short vowels. The changes in the final vowel of this word is caused by the position and function of the word itself.
Now, when writing one does not usually insert vowels, and whatever the last vowel of a word as long as it is single, it does not affect the way the word is written. But when a word is indefinite it takes a doubled vowel on its last letter, and if that final vowel is a ــًـ it must be followed by an ا, and this affects the way the word is written, which in turn affects the way the reader understands the word, as he/she will consider it ending in ــٌـ or ــٍـ in the event the ا is omitted.
Analysis of the examples
In the first sentence above, الكتاب is the subject of a nominal sentence and therefore takes a ــُـ on its last letter.
In the second sentence, الكتاب is the direct object of the verb اشتريت (which means "I bought"), and thus takes a ــَـ as the final vowel.
In the third sentence, الكتاب follows a preposition and as such its final letter must be vowelled with a ــِـ. The same goes for the last sentence.
Single/Double final vowels
The noun الكتاب in all the above sentences is definite, that's why the changing final vowel is always single; were it indefinite, the vowel would have been double.
Which vowel is affected?
This change in final vowel is called declension. Declension mostly affects the final vowel, but sometimes instead of the last vowel it affects a letter, final or not.
When to use which vowel?
ــَـ as final vowel
The final vowel should be a ــَـ or ــًـ when the noun is a direct object.
ــُـ as final vowel
The final vowel should be a ــُـ or ــٌـ when the noun is the subject of a verb, of the subject (or predicate) of a nominal sentence.
ــِـ as final vowel
The final vowel should be a ــِـ or ــٍـ when the noun comes after a preposition or is in the second position in a possessive construct.