In short

English needs two devices to grade an adjective - the endings -er / -est for short words (big, bigger, biggest) and the helpers more / most for long ones (more useful, most useful) - plus a bag of irregulars (good, better, best). Arabic needs one word shape. Take the three root letters of the adjective and pour them into the pattern أَفْعَلُ: كَبيرٌ becomes أَكْبَرُ, جَميلٌ becomes أَجْمَلُ, سَهْلٌ becomes أَسْهَلُ. That single form covers both “bigger” and “biggest”. Arabic grammar calls it اسْمُ التَّفْضيل, “the noun of preference”.

So the work of this lesson splits in two. First, building أَفْعَلُ - straightforward from a sound root, with two small irregular classes (doubled roots such as قَليلٌ → أَقَلُّ, and weak-final roots such as عالٍ → أَعْلى) and one suppletive pair, خَيْرٌ and شَرٌّ. Second, the frame you put it in: أَفْعَلُ + مِنْ makes a comparative, while الـ or an إِضافَة makes it a superlative. One ending fact runs through everything: an indefinite أَفْعَلُ never takes tanwīn, and its genitive is a fatḥa, not a kasra.

The rule

1. One shape, two jobs. أَفْعَلُ by itself is neither “bigger” nor “biggest” - the sentence around it decides. أَكْبَرُ مِنْ أَخي is “bigger than my brother”; الأَخُ الأَكْبَرُ is “the biggest/eldest brother”; أَكْبَرُ بَيْتٍ is “the biggest house”. Learn the shape once and the two meanings come free.

2. Building it from a sound triliteral. Pull out the three root letters and set them as أَ-فْ-عَ-لُ: a hamza with fatḥa, the first radical with sukūn, the second with fatḥa, the third with the case ending. The long vowel of the adjective disappears completely.

• كَبيرٌ (ك ب ر) → أَكْبَرُ - صَغيرٌ (ص غ ر) → أَصْغَرُ
• جَميلٌ (ج م ل) → أَجْمَلُ - طَويلٌ (ط و ل) → أَطْوَلُ
• سَهْلٌ (س ه ل) → أَسْهَلُ - كَثيرٌ (ك ث ر) → أَكْثَرُ

Note أَطْوَلُ: the و is the middle radical of ط و ل, and in the elative it stays a plain consonant with a sukūn - it is never contracted away. The pattern is stronger than the adjective you started from.

3. Doubled roots (المُضَعَّف) merge into one letter with a shadda. When the second and third radicals are the same, this pattern does not spell them out separately. The two collapse, the shadda appears, and the fatḥa that would have sat on the second radical slides back:

قَليلٌ (ق ل ل) → أَقَلُّ, never *أَقْلَلُ. هامٌّ / مُهِمٌّ (ه م م) → أَهَمُّ. شَديدٌ (ش د د) → أَشَدُّ. عَزيزٌ (ع ز ز) → أَعَزُّ. لَذيذٌ (ل ذ ذ) → أَلَذُّ.

4. Weak-final roots (النّاقِص) end in أَلِف مَقْصورَة and stop declining. When the third radical is و or ي, the elative ends in ـى, and that ending is fixed: أَعْلى is written and pronounced the same as subject, as object and after a preposition. Nothing is ever added to it - no ḍamma, no fatḥa, no tanwīn.

عالٍ (ع ل و) → أَعْلى, غالٍ (غ ل و) → أَغْلى, حُلْوٌ (ح ل و) → أَحْلى, قَوِيٌّ (ق و ي) → أَقْوى, ذَكِيٌّ (ذ ك ي) → أَذْكى, غَنِيٌّ (غ ن ي) → أَغْنى.

5. خَيْرٌ and شَرٌّ: the pair with no أَفْعَل. “Good/better/best” and “bad/worse/worst” are supplied by two words that do not show the أَفْعَلُ shape - historically they are elatives that lost their hamza (أَخْيَرُ → خَيْرٌ، أَشَرُّ → شَرٌّ). Because they look like ordinary nouns, they decline like ordinary nouns and do take tanwīn:

• الصِّحَّةُ خَيْرٌ مِنَ المالِ. - Health is better than money.
• الصَّمْتُ خَيْرٌ مِنْ كَلامٍ بِلا فائِدَةٍ. - Silence is better than pointless talk.
• التَّأْخيرُ شَرٌّ مِنَ الغِيابِ. - Being late is worse than being absent.

Everyday MSA also has two perfectly regular rivals: أَفْضَلُ (from فاضِلٌ / فَضيلٌ) and أَسْوَأُ (from سَيِّئٌ), and these are what you will hear most often. Use أَفْضَلُ / أَسْوَأُ freely; read خَيْرٌ / شَرٌّ, which are commoner in proverbs and formal prose.

6. The comparative: أَفْعَلُ + مِنْ, and the form never moves. This is the point where learners of European languages over-work. اسْمُ التَّفْضيل in a comparative is invariable - one shape for a man, a woman, two people, a crowd:

• هُوَ أَكْبَرُ مِنْ أَخيهِ. - هِيَ أَكْبَرُ مِنْ أُخْتِها. - هُمْ أَكْبَرُ مِنّا.

مِنْ is the one word Arabic uses for “than” - there is no second option to choose between. Before الـ it takes a helping fatḥa: أَكْبَرُ مِنَ البَيْتِ. With a pronoun it fuses: مِنّي، مِنْكَ، مِنْهُ، مِنْها، مِنّا، مِنْهُمْ.

The comparative can also sit inside a noun phrase as an ordinary adjective: أُريدُ حَقيبَةً أَكْبَرَ, “I want a bigger bag” - and there مِنْ is simply left off.

7. The ending: one ḍamma, no tanwīn, fatḥa for the genitive. أَفْعَلُ belongs to a class of nouns that refuse tanwīn. Say it as a slogan: one ḍamma, never two. So it is أَكْبَرُ, not *أَكْبَرٌ. And - the part that surprises everyone - after a preposition the ending is a fatḥa:

• سَكَنّا في بَيْتٍ أَكْبَرَ. - We lived in a bigger house.
• بَحَثْتُ عَنْ سِعْرٍ أَقَلَّ. - I looked for a lower price.

Two situations cancel this and bring the ordinary kasra back: when the word carries الـ, and when it is the first term of an إِضافَة.

• مِنَ البَيْتِ الأَكْبَرِ - في أَكْبَرِ مَدينَةٍ

(The class has a name, المَمْنوعُ مِنَ الصَّرْفِ, and a longer membership list; lesson 41 handles it. Here just memorise the behaviour of أَفْعَلُ.)

8. Superlative, shape 1: الأَفْعَلُ / الفُعْلى - a normal agreeing adjective. Put الـ on the elative, attach it to a definite noun, and it behaves exactly like any adjective of lesson 8: same gender, same number, same case. The feminine of أَفْعَلُ is فُعْلى:

• الأَخُ الأَكْبَرُ - the eldest brother - الأُخْتُ الكُبْرى - the eldest sister
• الشَّرْقُ الأَوْسَطُ - the Middle East - الدُّوَلُ الكُبْرى - the great powers

In everyday MSA فُعْلى is in real use for only a limited set - الكُبْرى، الصُّغْرى، العُظْمى، الوُسْطى، العُلْيا، الدُّنْيا، القُصْوى - plus a few fixed phrases (الحُسْنى، المُثْلى), so treat it as vocabulary rather than as a rule you apply to any elative. And note that فُعْلى belongs to the superlative only: a comparative with مِنْ never uses it.

9. Superlative, shape 2: أَفْعَلُ + an indefinite singular in the genitive. No article anywhere; the elative is the first term of an إِضافَة, and the noun after it is singular, indefinite and مَجْرور. This is the workhorse of headlines and everyday speech:

• أَكْبَرُ مَدينَةٍ - the biggest city - أَهَمُّ سُؤالٍ - the most important question
• أَعْلى جَبَلٍ - the highest mountain - أَسْرَعُ طَريقٍ - the fastest route

The elative here is invariable for gender: هِيَ أَذْكى طالِبَةٍ, not *ذُكْيا.

10. Superlative, shape 3: أَفْعَلُ + a definite plural in the genitive. Same إِضافَة, but the second term is a definite plural. The meaning is “the …-est of the …”:

• أَكْبَرُ المُدُنِ - the biggest of the cities - أَطْوَلُ الأَنْهارِ - the longest of the rivers - أَفْضَلُ الطُّلّابِ - the best of the students

Shapes 2 and 3 mean much the same thing; shape 2 is the more frequent. What you may not do is mix either with مِنْ - the إِضافَة already carries the “of”.

11. When there is no أَفْعَل to build: أَكْثَرُ / أَشَدُّ + an accusative noun. Two families of adjectives cannot produce an elative. Colours and physical traits are already on the أَفْعَلُ pattern (أَحْمَرُ، أَزْرَقُ، أَعْمى), and adjectives derived from the longer verb forms are too long to compress (مُزْدَحِمٌ، مُفيدٌ، مُنَظَّمٌ). For both, Arabic grades a helper word instead - usually أَكْثَرُ (“more in quantity”) or أَشَدُّ (“more in intensity”) - and turns the adjective into a noun in the accusative:

• هٰذِهِ الوَرْدَةُ أَشَدُّ حُمْرَةً مِنْ تِلْكَ. - This rose is redder than that one.
• الشّارِعُ أَكْثَرُ اِزْدِحامًا في الصَّباحِ. - The street is more crowded in the morning.
• الكِتابُ الثّاني أَكْثَرُ فائِدَةً. - The second book is more useful.

The accusative noun is a تَمْييز, “a specification”; lesson 61 explains the case. For now copy the frame: helper in the elative, adjective-turned-noun with ـً.

12. Two small extras. To say how much more, add بِـ + amount after the elative: أَكْبَرُ بِكَثيرٍ (much bigger), أَغْلى بِقَليلٍ (slightly dearer), أَكْبَرُ مِنّي بِسَنَتَيْنِ (two years older than me). And for “as … as” - equality, not comparison - the elative is not used at all: هُوَ طَويلٌ مِثْلَ أَخيهِ.

Forms & patterns

Sound triliteral adjectives

The two irregular classes, and the suppletive pair

Declension of أَكْبَرُ - one ḍamma, and a fatḥa where you expect a kasra

أَعْلى and the other ناقِص elatives have a single form in all nine cells.

Superlative with الـ - it agrees like any adjective

The high-frequency فُعْلى feminines - learn them as words

No أَفْعَل available - grade a helper instead

Left out of these tables: the rare masculine plural الأَفْعَلونَ, and the press habit of putting the feminine plural first (كُبْرَياتُ الشَّرِكاتِ, “the largest companies”) - read them, do not build them yet.

Examples

Common mistakes

• هُوَ أَكْبَرٌ مِنْ أَخيهِ. -> هُوَ أَكْبَرُ مِنْ أَخيهِ. - أَفْعَلُ never takes tanwīn. One ḍamma, never two; the same for أَقَلُّ، أَهَمُّ، أَسْوَأُ.
• هِيَ كُبْرى مِنْ أُخْتِها. -> هِيَ أَكْبَرُ مِنْ أُخْتِها. - the feminine فُعْلى is for the superlative only. In a comparative with مِنْ the elative does not agree with anything.
• هُمْ أَكْبَرونَ مِنّا. -> هُمْ أَكْبَرُ مِنّا. - no plural either. The comparative has exactly one form for every subject.
• سَكَنّا في بَيْتٍ أَكْبَرٍ. -> سَكَنّا في بَيْتٍ أَكْبَرَ. - an indefinite أَفْعَلُ takes a fatḥa in the genitive. The kasra comes back only with الـ (البَيْتِ الأَكْبَرِ) or in an إِضافَة (في أَكْبَرِ بَيْتٍ).
• هٰذا الأَكْثَرُ جَميلٌ. -> هٰذا الأَجْمَلُ. - Arabic does not stack “most” in front of an ordinary adjective. Build the one word أَفْعَلُ; أَكْثَرُ / أَشَدُّ appear only when no أَفْعَلُ can be built.
• أَقْلَلُ مِنْ ذٰلِكَ -> أَقَلُّ مِنْ ذٰلِكَ - in this pattern a doubled root writes its repeated letter once, with a shadda. Likewise أَهَمُّ, not *أَهْمَمُ.
• هُوَ أَغْلًى مِنْ هٰذا. -> هُوَ أَغْلى مِنْ هٰذا. - elatives ending in أَلِف مَقْصورَة carry no vowel and no tanwīn at all, in any case.
• هِيَ أَكْبَرُ مِنَ المُدُنِ. -> هِيَ أَكْبَرُ المُدُنِ. - the superlative إِضافَة already means “of”; adding مِنْ turns it back into a comparison with the cities.
• أَكْبَرُ مَدينَةً في العالَمِ -> أَكْبَرُ مَدينَةٍ في العالَمِ - the second term of an إِضافَة is genitive, and it stays singular and indefinite.
• هٰذِهِ الوَرْدَةُ أَحْمَرُ مِنْ تِلْكَ. -> هٰذِهِ الوَرْدَةُ أَشَدُّ حُمْرَةً مِنْ تِلْكَ.
  • أَحْمَرُ is already on the أَفْعَلُ pattern, so it cannot be graded again.
• الشّارِعُ أَكْثَرُ اِزْدِحامٌ. -> الشّارِعُ أَكْثَرُ اِزْدِحامًا. - the noun after أَكْثَرُ / أَشَدُّ is accusative, with ـً.

Tips

• Store the pair, not the single word: كَبيرٌ / أَكْبَرُ، قَليلٌ / أَقَلُّ، عالٍ / أَعْلى. The elative is regular enough to derive, but it is faster to have it ready.
• Chant the ending as a two-word rule - “one ḍamma, fatḥa after a preposition” - and drill the one phrase في بَيْتٍ أَكْبَرَ until it sounds normal. That single habit fixes the commonest error in the lesson.
• Test yourself with مِنْ: if مِنْ is there, the form is frozen; if الـ or a following noun is there, you are in the superlative and agreement or the genitive matters.
• Shape 2 (أَكْبَرُ مَدينَةٍ) is the one to make automatic. It is short, it never needs agreement, and it is everywhere in headlines: أَهَمُّ قَرارٍ، أَكْبَرُ شَرِكَةٍ، أَعْلى نِسْبَةٍ.
• Start the فُعْلى list from the seven words in the table and add others only as you meet them. Inventing a feminine for every elative produces forms nobody uses.
• When you are stuck for an elative - a long participle, a colour, a borrowed adjective - reach for أَكْثَرُ / أَشَدُّ + noun + ـً. It works for almost any adjective, as long as the noun behind it exists (اِزْدِحام، فائِدَة، حُمْرَة).
• Do not worry yet about why أَفْعَلُ refuses tanwīn, or about the case name of حُمْرَةً. Both have their own lessons later; the forms above are enough to speak and write now.