What is a mamdūd ism?
صَحْرَاءُ، حَسْنَاءُ، عُلَمَاءُ، أَسْمَاءٌ، اِبْتِغَاءٌ — all end in ـَاء, and they do not all behave alike.
Unlike the maqṣūr and the manqūṣ, the mamdūd shows its vowels perfectly well. A hamza carries a ḍamma, a fatḥa or a kasra without difficulty. So the question here is not how it shows i'rab — it is whether the word is fully or partly declining.
Seven categories that express i'rab their own way — by letters instead of vowels, or by not showing it at all.
That turns on the kind of hamza. When the hamza stands for the feminine ending — صَحْرَاءُ، حَسْنَاءُ، عُلَمَاءُ — one cause is enough to stop the word, and it becomes partly declining: no tanwīn, a fatḥa in jarr.
When the hamza belongs to the root or the pattern — أَسْمَاءٌ، أَنْبَاءٌ، اِبْتِغَاءٌ — the word is perfectly ordinary and takes tanwīn like any other.
| The hamza stands for | The word is | |
|---|---|---|
| the feminine ending | partly declining — no tanwīn, fatḥa in jarr | صَحْرَاءُ، حَسْنَاءُ، عُلَمَاءُ |
| a letter of the root or the pattern | fully declining — tanwīn, kasra in jarr | أَسْمَاءٌ، أَنْبَاءٌ، اِبْتِغَاءٌ |
Both columns end in ـَاء and look identical. The ending tells you nothing; only the kind of hamza does.
This is the most common trap in the whole of this topic, and it catches good students.
Not every ـَاء ending makes a word partly declining.
أَنْبَاءٌ، أَسْمَاءٌ، أَنْحَاءٌ، اِبْتِغَاءٌ all end in ـَاء and all take tanwīn quite normally.
The book that treats this most carefully raises it as a warning in its own right: students assume the ending alone decides, and it does not. The hamza has to be the feminine hamza, sitting after an added alif.
Learn to tell the two hamzas apart and this whole class of error disappears.