In short

“Twenty students”, “a kilo of honey”, “two years older”, “richer in oil”: in each of these the first word is vague on its own, and a second word arrives to say what is being counted, weighed or compared. English does that four different ways; Arabic does it with one ending. Put the clarifying noun in the accusative, keep it singular, keep it indefinite, and you are done: عِشْرونَ طالِبًا “twenty students”, أَكْبَرُ سِنًّا “older in age”. That accusative is التَّمْييز, “the distinguisher”.

Two things make it worth a lesson of its own. First, you have been using half of it since lesson 26 without a name for it - the counted noun after 11-99 is a تَمْييز. Second, modern written Arabic has concentrated the construction into one very productive frame: an elative plus a تَمْييز - الأَكْثَرُ مَبيعًا “best-selling”, الأَفْضَلُ أَداءً “best-performing”, أَكْثَرُ الدُّوَلِ إِنْتاجًا “the most productive country”. On the page it looks exactly like a حال from lesson 55, and a short test tells the two apart.

The rule

1. The definition, and the question it answers. التَّمْييز is a noun that removes the vagueness - الإِبْهامُ - of what came just before it. Its question is not “how?” but مِنْ أَيِّ ناحِيَةٍ؟, “in what respect?”. Three properties define it, and the first two never bend:

• مَنْصوبٌ - accusative; the fatḥatān is the only mark of the relation.
• نَكِرَةٌ - indefinite. No الـ, no إِضافَة, no attached pronoun.
• مُفْرَدٌ - singular, whatever the number or gender of the word it explains. The point of the rule is that it never copies anything; a few fillers happen to be plural nouns in their own right (أَكْثَرُ الدُّوَلِ سُكّانًا), and even those agree with nothing.

A fourth property is a very strong tendency rather than a law: the filler is a جامِدٌ noun - a plain noun (ماءً، قَمْحًا، سِنًّا) or a مَصْدَر from lesson 54 (اِجْتِهادًا، إِنْتاجًا، حَرارَةً). A participle in the slot normally points to a حال instead - the press’s frozen مَبيعًا is the one common exception. That is where الحال goes the other way, and section 9 turns it into a test.

2. The two types. Arabic sorts تَمْييز by how much it clarifies:

• تَمْييزُ المُفْرَدِ (also تَمْييزُ الذّاتِ) clarifies one word right in front of it - a number, a weight, a volume, an area. عِشْرونَ is vague until طالِبًا lands.
• تَمْييزُ النِّسْبَةِ (also تَمْييزُ الجُمْلَةِ) clarifies the whole clause. In اِزْدادَ الطّالِبُ اجْتِهادًا nothing is vague about الطّالِبُ; what is vague is the claim that he “increased” - increased in what? اجْتِهادًا answers it.

3. Type one: after a quantity. Four families, all behaving identically:

• العَدَدُ - the numbers. عِشْرونَ طالِبًا، خَمْسَةَ عَشَرَ كِتابًا، اِثْنانِ وأَرْبَعونَ يَوْمًا.
• الوَزْنُ - weight. كيلوغْرامٌ عَسَلًا، طُنٌّ قَمْحًا.
• الكَيْلُ - volume and measure. لِتْرٌ زَيْتًا، صُنْدوقٌ بُرْتُقالًا.
• المِساحَةُ - area and length. هَكْتارٌ قُطْنًا، مِتْرٌ قُماشًا.

Interrogative كَمْ from lesson 15 behaves the same way: كَمْ كِتابًا قَرَأْتَ؟

4. Numbers: a recap, not a new rule. Lesson 26 gave you the polarity and the three regimes; nothing here changes them. Only the label is new: of the three regimes, 11-99 is the one that puts the counted noun in the accusative, and that is a تَمْييز in this lesson’s technical sense. After 3-10 and after مِائَة / أَلْف the counted noun is genitive as the second term of an إِضافَة, and lesson 26 calls it تَمْييز in the looser sense of “the noun the number counts”.

5. What modern prose actually writes for measures. The accusative after a measure word is correct and you will meet it in careful writing, but today’s default is the preposition مِنْ: كيلو مِنَ العَسَلِ، لِتْرٌ مِنَ الزَّيْتِ، كوبٌ مِنَ الشّايِ. An إِضافَة is just as normal in the shops: كيلوغْرامُ عَسَلٍ. So recognise the accusative and produce مِنْ. The numbers are the exception - عِشْرونَ طالِبًا has no مِنْ variant, and the accusative is obligatory.

6. Type two, converted from the فاعِل. A family of verbs of increase, decrease, filling, overflowing and being-good states the subject first and then names the respect. The traditional analysis is that the تَمْييز was originally the فاعِل and has swapped places with it:

• اِزْدادَ الطّالِبُ اجْتِهادًا ← اِزْدادَ اجْتِهادُ الطّالِبِ.
• حَسُنَ الطّالِبُ خُلُقًا ← حَسُنَ خُلُقُ الطّالِبِ.
• فاضَ النَّهْرُ ماءً ← فاضَ ماءُ النَّهْرِ.
• اِمْتَلَأَ الكوبُ ماءً.

The conversion is not something you perform in order to write the sentence; it is a way of seeing why the noun is neither a subject nor an object. What you do need is the verb list, because the construction is lexical: اِزْدادَ، زادَ، اِمْتَلَأَ، فاضَ، حَسُنَ، طابَ، اِشْتَدَّ. زادَ الأَمْرُ تَعْقيدًا “the matter got more complicated” is a staple of Arabic journalism.

7. Type two, converted from the مَفْعولِ بِهِ. The same swap, but with a transitive verb whose object is already in place:

• زَرَعْتُ الأَرْضَ قَمْحًا ← زَرَعْتُ قَمْحَ الأَرْضِ.
• مَلَأْتُ الكوبَ ماءً ← مَلَأْتُ ماءَ الكوبِ.

The “original” here is frankly a grammarians’ reconstruction - nobody writes مَلَأْتُ ماءَ الكوبِ. Treat the arrow as a diagnostic, not as a style model.

8. Type two after اسْمِ التَّفْضيلِ - the frame to master. This is where تَمْييز lives in modern Arabic, and it deserves more of your practice time than everything above. An elative from lesson 28 is vague in exactly the way a number is: أَكْبَرُ - bigger in what?

• Comparative: أَخي أَكْبَرُ سِنًّا مِنّي. The تَمْييز may sit before or after مِنْ: أَكْبَرُ مِنّي سِنًّا is just as good.
• Superlative with الـ: الرِّوايَةُ الأَكْثَرُ مَبيعًا، الفَريقُ الأَفْضَلُ أَداءً، الطَّريقُ الأَقَلُّ تَكْلِفَةً. This is the press’s standard way of forming an English-style compound adjective.
• Superlative with an إِضافَة: أَكْثَرُ الدُّوَلِ إِنْتاجًا، أَكْثَرُ المُدُنِ ازْدِحامًا. Note where the accusative falls: the إِضافَة ends at الدُّوَلِ, and the تَمْييز stands outside it with its own fatḥatān.
• The no-elative repair from lesson 28 §11: adjectives that cannot form أَفْعَلُ are graded with أَكْثَرُ / أَشَدُّ / أَقَلُّ plus their مَصْدَر - أَشَدُّ حَرارَةً، أَكْثَرُ ازْدِحامًا، أَقَلُّ رُطوبَةً. That accusative was always a تَمْييز; now you know why it is there.

Two details catch people out. The elative still takes whatever case the sentence gives it (هُوَ الأَكْثَرُ خِبْرَةً، رَأَيْتُ الأَكْثَرَ خِبْرَةً), while the تَمْييز never moves off the fatḥa. And it never agrees with anything, so a plural changes nothing: الكُتُبُ الأَكْثَرُ مَبيعًا, never *مَبيعاتٍ.

9. Telling it from الحال. Both are indefinite accusatives hanging off the end of a complete sentence, and the deletion test does not separate them - you can drop either. Three things do:

• Word type. الحال is مُشْتَقّ, a participle or an adjective; التَّمْييز is جامِد, a plain noun or a مَصْدَر. This is the fastest test, and it decides all but a handful of cases.
• What it describes. الحال describes the doer or the thing; التَّمْييز names the respect in which a statement holds.
• Agreement. الحال agrees in gender and number; التَّمْييز never does.

The pair to keep in your head: عادَ الجُنودُ مُنْتَصِرينَ - the soldiers came back victorious, a state of theirs, derived, plural to match them. Against اِزْدادَ الجَيْشُ عَدَدًا - the army grew in number, a plain noun naming the dimension, singular whatever the army does.

10. Telling it from the مَفْعولِ بِهِ. اِمْتَلَأَ الكوبُ ماءً looks like a verb with an object, and learners duly write *اِمْتَلَأَ الكوبُ الماءَ. Two checks. The verb: اِمْتَلَأَ is لازِم (lesson 30), so there is no object slot to fill. And definiteness: an object may carry الـ, a تَمْييز may not. In مَلَأْتُ الكوبَ ماءً the object slot is visibly taken by الكوبَ, which leaves ماءً no other job.

11. Writing the ending. The same three spellings as in lesson 55: a prop alif on an ordinary consonant (كِتابًا، قَمْحًا), the tanwīn on the ة with no alif (حَرارَةً، تَكْلِفَةً), and the tanwīn on the hamza after a long alif (ماءً، أَداءً). Because the slot is indefinite and copies nothing, no dual or sound-plural ending is ever needed here. And the prop-alif spelling survives the pausal form as an audible ā - the ة type has no alif to fall back on and stops as حَرارَهْ - so this is a case ending you will really hear.

One further accusative is still to come: the noun after إِلّا in an exception. That belongs to lesson 62 and follows entirely different rules - do not treat it as a تَمْييز.

Forms & patterns

The two types side by side

Type one: quantities, and what modern prose prefers

The numbers - recap only; lesson 26 has the full grid

Type two: the conversion that explains the case

The verbs that take a تَمْييزُ نِسْبَةٍ

The elative frames - the productive core

التَّمْييز against الحال

Writing the accusative ending

Examples

Common mistakes

• عِشْرونَ كُتُبًا -> عِشْرونَ كِتابًا - after 11-99 the تَمْييز is singular. Arabic counts in single items: “twenty as far as a book is concerned”.
• عِشْرونَ كِتابٌ -> عِشْرونَ كِتابًا - and accusative. The ḍamma turns the noun into a second subject, and the number is left with nothing to specify it.
• اِمْتَلَأَ الكوبُ الماءَ -> اِمْتَلَأَ الكوبُ ماءً - a تَمْييز is indefinite, always. اِمْتَلَأَ is intransitive as well, so الماءَ could not be an object either.
• أَكْثَرُ سُكّانٌ -> أَكْثَرُ سُكّانًا - after an elative the fatḥatān is the only thing linking the two words. Without it the phrase falls apart.
• أَخي أَكْبَرُ في السِّنِّ -> أَخي أَكْبَرُ سِنًّا - the elative asks for a bare accusative, not a prepositional phrase. (أَكْبَرُ مِنّي في السِّنِّ is heard in modern prose, but the تَمْييز is the frame this lesson trains and the one that always works.)
• الكُتُبُ الأَكْثَرُ مَبيعاتٍ -> الكُتُبُ الأَكْثَرُ مَبيعًا - a تَمْييز never agrees with anything. Plural owner, singular تَمْييز.
• اِزْدادَ الطّالِبُ مُجْتَهِدًا -> اِزْدادَ الطّالِبُ اجْتِهادًا - the slot takes a جامِد noun, here a مَصْدَر. A participle in it would be read as a حال and say something else.
• الجَوُّ أَشَدُّ حارًّا -> الجَوُّ أَشَدُّ حَرارَةً - the same point inside the elative frame: convert the adjective to its noun (حارٌّ → حَرارَةٌ) before you put the fatḥa on it.
• أَكْثَرُ الدُّوَلِ إِنْتاجٍ -> أَكْثَرُ الدُّوَلِ إِنْتاجًا - the إِضافَة stops at الدُّوَلِ. The تَمْييز stands outside it and keeps its own accusative.
• كيلوغْرامٌ عَسَلٍ -> كيلوغْرامٌ عَسَلًا - pick one structure and finish it: with the tanwīn on the measure word the noun after it is a تَمْييز, as an إِضافَة it is كيلوغْرامُ عَسَلٍ, and in ordinary modern prose it is كيلو مِنَ العَسَلِ.

Tips

• One question does the recognising: “in what respect?”. If the answer is a bare noun with a fatḥatān and no preposition, you are looking at a تَمْييز.
• Chant the three properties as one word - singular-indefinite-accusative. Every learner error in this lesson is one of the three going wrong.
• Put your practice into the elative frame, where the construction actually lives today. Ten ready-made chunks will carry you a long way: أَكْبَرُ سِنًّا، أَكْثَرُ سُكّانًا، أَكْثَرُ اسْتِخْدامًا، الأَكْثَرُ مَبيعًا، الأَفْضَلُ أَداءً، الأَعْلى دَخْلًا، أَشَدُّ حَرارَةً، أَقَلُّ تَكْلِفَةً، أَسْرَعُ نُمُوًّا، أَوْسَعُ انْتِشارًا.
• For measures, split your skills: produce مِنْ (كوبٌ مِنَ الشّايِ), recognise the accusative (كوبٌ شايًا). Both are correct; one sounds current.
• The جامِد / مُشْتَقّ test against الحال is quicker than any meaning test. Noun in the slot -> تَمْييز. Participle in the slot -> حال, the elative’s frozen مَبيعًا aside.
• Say the ـً out loud wherever it is written with a prop alif. Of the three tanwīns it is the one that survives a pause, so it is audible even from a speaker who drops every other case ending.
• Reading unvocalized text, do not go hunting: تَمْييز has three shapes on the page - after a quantity, after an elative, and after a verb of increase or filling. Everything else parses as something else.
• Keep إِلّا out of this box. The accusative after an exception is lesson 62 and has its own conditions.