The Decades 20–90 | Arabic (Modern Standard) Grammar

The round decades from twenty through ninety form another distinct number system in formal Modern Standard Arabic. They do not show gender polarity: the same عشرون counts masculine and feminine nouns. They do show case through endings like those of the sound masculine plural: nominative ـون contrasts with accusative/genitive ـين. The counted noun is an indefinite singular accusative specification, as in عشرون طالبا and عشرون طالبة.

The forms on this page are standard in edited writing and careful speech (formal). Case endings are especially audible in news, speeches, and formal reading. Regional varieties often use a single oblique-like form or a different pronunciation (regional: varies), but those systems should not replace MSA case in formal prose.

The decade forms

Each decade has a nominative form in ـون and one shared accusative/genitive form in ـين.

Value	Nominative	Accusative / genitive
20	عشرون	عشرين
30	ثلاثون	ثلاثين
40	أربعون	أربعين
50	خمسون	خمسين
60	ستون	ستين
70	سبعون	سبعين
80	ثمانون	ثمانين
90	تسعون	تسعين

Saying that they decline “like sound masculine plurals” describes their case endings; it does not make them ordinary human plural nouns. Unlike an adjective such as معلمون, a decade does not change to a feminine plural form when it counts women.

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Read the final long vowel before choosing the noun: -ūna marks nominative, while -īna marks both accusative and genitive. Gender never decides between them.

Nominative ـون

Use the ـون form when the whole number phrase is nominative—for example, as the subject of a verb or the predicate of a nominal sentence.

شارك عشرون محاميا في الجلسة الافتتاحية.

shāraka ʿishrūna muḥāmiyan fī l-jalsati l-iftitāḥiyya(h).

Twenty lawyers took part in the opening session.

عشرون is nominative because the number phrase is the subject. محاميا does not copy that case: it is the singular accusative specification of the numeral.

تعمل ثلاثون مهندسة في المرحلة الأولى من المشروع.

taʿmalu thalāthūna muhandisatan fī l-marḥalati l-ʾūlā mina l-mashrūʿ.

Thirty female engineers are working in the first phase of the project.

Feminine مهندسة still takes ثلاثون, not a special feminine decade. The word after the decade remains singular accusative مهندسةً.

المسافة أربعون كيلومترا تقريبا.

al-masāfatu ʾarbaʿūna kīlūmitran taqrībā.

The distance is approximately forty kilometers.

Here أربعون كيلومترا is the predicate and therefore nominative. This measurement expression shows why the numeral and unit must be parsed together: أربعون carries the outer case; singular كيلومترا identifies the unit.

Accusative and genitive ـين

Use ـين when the number phrase is a direct object or another accusative constituent, and also after a preposition or other genitive governor.

دعت المؤسسة عشرين محامية إلى ورشة التفاوض.

daʿati l-muʾassasatu ʿishrīna muḥāmiyatan ʾilā warshati t-tafāwuḍ.

The organization invited twenty female lawyers to the negotiation workshop.

تحدث الباحث مع ثلاثين مشاركا بعد التجربة.

taḥaddatha l-bāḥithu maʿa thalāthīna mushārikan baʿda t-tajriba(h).

The researcher spoke with thirty participants after the experiment.

Direct-object عشرين and genitive ثلاثين share ـين. The case difference is syntactic rather than visible in the decade's form.

دفعت خمسين دولارا لتجديد الاشتراك.

dafaʿtu khamsīna dūlāran li-tajdīdi l-ishtirāk.

I paid fifty dollars to renew the subscription.

استمر المعرض ثلاثين يوما دون انقطاع.

ʾistamarra l-maʿriḍu thalāthīna yawman dūna nqiṭāʿ.

The exhibition lasted thirty days without interruption.

The price and duration are accusative expressions, so the decades use خمسين and ثلاثين. دولارا and يوما remain singular accusative; English plural dollars/days should not trigger an Arabic plural here.

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Case is divided across two layers: the decade reflects the phrase's job in the sentence, but its counted noun is always accusative tamyīz. Thus مع ثلاثين طالبا has a genitive numeral and an accusative specification.

Gender stays invariant

The decade does not inspect the noun's gender. Only the specification and any adjective describing it show the noun's ordinary gender agreement.

شارك ستون متطوعا وستون متطوعة في الحملة.

shāraka sittūna mutaṭawwiʿan wa-sittūna mutaṭawwiʿatan fī l-ḥamla(h).

Sixty male volunteers and sixty female volunteers took part in the campaign.

Both subject phrases use nominative ستون. Masculine متطوعا and feminine متطوعةً distinguish the groups; the numeral does not.

تضم القاعدة تسعين صورة عالية الدقة.

taḍummu l-qāʿidatu tisʿīna ṣūratan ʿāliyata d-diqqa(h).

The database contains ninety high-resolution images.

The adjective عالية agrees with singular feminine صورة, not with the mathematical plurality. This singular agreement follows directly from the form of the specification.

Reading digits as a governed phrase

Digits are frequent in reports and interfaces (formal/technical). When read aloud, a digit inherits the case and noun pattern of its sentence.

سجل النظام ٤٠ طلبا، أي أربعين طلبا، خلال ساعة.

sajjala n-niẓāmu ʾarbaʿīna ṭalaban, ʾay ʾarbaʿīna ṭalaban, khilāla sāʿa(h).

The system recorded 40 requests—that is, forty requests—within an hour.

Because ٤٠ طلبا is the direct object, 40 is read أربعين, not nominative أربعون. The digits retain the value forty inside right-to-left text; they are not reversed into four.

A controlled look at coordination with units

For 21–99 outside the teens, Arabic places the unit first, then و, then the decade: literally “three and twenty.” The counted noun is still singular accusative. The unit follows its own gender and case rules, while the decade shows ـون/ـين.

وصل ثلاثة وعشرون كتابا إلى المخزن.

waṣala thalāthatun wa-ʿishrūna kitāban ʾilā l-makhzan.

Twenty-three books arrived at the warehouse.

وصلت ثلاث وعشرون رسالة إلى القسم.

waṣalat thalāthun wa-ʿishrūna risālatan ʾilā l-qism.

Twenty-three messages reached the department.

Masculine كتاب selects polarity-marked ثلاثة, whereas feminine رسالة selects ثلاث; nominative عشرون is unchanged. This is only the structural preview. One, two, case on coordinated units, and the full 21–99 paradigm are covered on 21–99: Coordinating Units and Decades.

Common Mistakes

Using nominative ـون after a preposition

❌ تحدثت مع عشرون موظفا.

Incorrect — after مع, twenty must be genitive عشرين.

✅ تحدثت مع عشرين موظفا.

taḥaddathtu maʿa ʿishrīna muwaẓẓafā.

I spoke with twenty employees.

Using nominative ـون as a direct object

❌ دفعت خمسون دولارا.

Incorrect — the amount paid is accusative, so fifty is خمسين.

✅ دفعت خمسين دولارا.

dafaʿtu khamsīna dūlārā.

I paid fifty dollars.

Pluralizing the counted noun

❌ حضر عشرون طلابا.

Incorrect — after a decade, the counted noun is singular accusative.

✅ حضر عشرون طالبا.

ḥaḍara ʿishrūna ṭālibā.

Twenty students attended.

Putting the decade before the unit

❌ وصل عشرون وثلاثة كتابا.

Incorrect for 23 — Arabic coordinates the unit before the decade.

✅ وصل ثلاثة وعشرون كتابا.

waṣala thalāthatun wa-ʿishrūna kitābā.

Twenty-three books arrived.

Reversing the digits in right-to-left text

❌ الرقم ٤٠ يعني أربعة.

Incorrect — ٤٠ is forty; the zero still occupies the units place.

✅ الرقم ٤٠ يعني أربعين في هذا السياق.

ar-raqmu ʾarbaʿūna yaʿnī ʾarbaʿīna fī hādhā s-siyāq.

The number 40 is read as أربعين in this context.

Key Takeaways

The decades take nominative ـون and shared accusative/genitive ـين.
They are invariant for gender: عشرون طالبا and عشرون طالبة.
The counted noun is always an indefinite singular accusative specification.
A written digit must be read with the case required by its sentence position.
In coordinated 21–99 forms, the unit precedes و plus the decade; the full system is treated separately.

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