Ability and Obligation | Arabic (Modern Standard) Grammar

English can and must look like compact helper verbs, but formal Modern Standard Arabic divides their work among several constructions. أستطيع أن attributes ability to a person. Impersonal يمكن أن presents an event as possible, while يمكنني أن gives a person access or practical ability. يجب أن expresses a requirement, and ينبغي أن usually presents an advisable, expected, or normatively appropriate course.

The following verb is not an infinitive. After أنْ, it is an imperfect verb in the subjunctive and still marks person, gender, and number. The modal frame supplies possibility or force; the subordinate verb supplies the action and its participants. See أنْ + subjunctive clauses for the wider complement system.

A substitution map

Frame	What varies	Core meaning	Typical force/register
أستطيع أن + subjunctive	أحضر، نكمل، ترسلي	be able to	personal ability; neutral formal
يمكن أن + subjunctive	يتغير، تصل، يحدث	it is possible that	impersonal possibility; neutral formal
يمكن لـ / يمكنني أن	للطالب، لنا، ـني	it is possible/available for someone	permission or practical possibility
يجب أن + subjunctive	يصل، نراجع، تكتبي	must, it is necessary	firm obligation
يجب على + person + أن/maṣdar	الموظف، الزوار، علينا	someone is obliged	explicit duty-bearer
ينبغي أن + subjunctive	نتحقق، يوضح، تراجعي	should, ought to	formal advice or norm

Prepositional nouns after لـ and على are genitive. Attached forms fuse with the preposition: لي، لك، لنا and عليّ، عليك، علينا. With a sound singular, أنْ changes indicative أكتبُ to subjunctive أكتبَ. With the five verbs, it deletes nūn: ترسلين → أن ترسلي.

أستطيع أن: an ability belongs to its subject

اِسْتَطَاعَ / يَسْتَطِيعُ is a personal verb. Its subject is the person or entity able to perform the following action: أستطيع، تستطيع، يستطيع، نستطيع. The most dependable productive frame is أستطيع أن + subjunctive.

أستطيع أن أقرأ النص، لكنني لا أفهم كل مصطلح

ʾastaṭīʿu ʾan ʾaqraʾa n-naṣṣa, lakinnanī lā ʾafhamu kulla muṣṭalaḥ

I can read the text, but I do not understand every term. (Neutral formal.)

لن تستطيعوا أن تدخلوا المبنى بعد الثامنة

lan tastaṭīʿū ʾan tadkhulū l-mabnā baʿda th-thāmina

You will not be able to enter the building after eight. (Addressed to a male or mixed group.)

Both verbs in the second example lose nūn: لن تستطيعوا and أن تدخلوا. The first loss is governed by لن; the second by أنْ. The similar surface endings have separate syntactic causes.

Negative لا أستطيع الحضور often has the nonliteral English equivalent “I can't make it,” not merely “I lack the physical ability to attend.” The maṣdar الحضور can directly name the unavailable action.

أعتذر، لا أستطيع الحضور غدا

ʾaʿtadhiru, lā ʾastaṭīʿu l-ḥuḍūra ghadan

I'm sorry, I can't make it tomorrow. (Polite formal-neutral response.)

يمكن: possibility before a person

Impersonal يمكن أن + clause means “it is possible that / may.” It normally stays third-person masculine singular because the following clause is what is possible. The subordinate verb agrees with its own subject.

يمكن أن يتغير الموعد إذا تأخرت الرحلة

yumkinu ʾan yataghayyara l-mawʿidu ʾidhā taʾakhkharati r-riḥla

The time may change if the flight is delayed. (Impersonal possibility.)

To name the person for whom an action is possible, use يمكن لـ + person + أن... or an attached form such as يمكنني، يمكنك، يمكننا. In يمكنني أن أرسل, ـني does not turn يمكن into a first-person conjugation; the verb remains impersonal.

يمكن للزوار شراء التذاكر عبر الموقع

yumkinu liz-zuwwāri shirāʾu t-tadhākiri ʿabra l-mawqiʿ

Visitors can buy tickets through the website. (The maṣdar شراء is the possible action.)

يمكنني أن أرسل إليك النسخة هذا المساء

yumkinunī ʾan ʾursila ʾilayka n-nuskhata hādhā l-masāʾ

I can send you the copy this evening. (Practical availability.)

💡

Use أستطيع when ability is a property of an explicit subject. Use يمكن when you first present an event, option, or access as possible. Many contexts permit both, but the information structure is different.

يجب: necessity and the duty-bearer

يجب أن + clause presents the event as necessary. When context already identifies who must act, no separate person phrase is needed. To name the duty-bearer explicitly, use يجب على + person + أن... or يجب على + person + maṣdar.

يجب أن يصل الطلب قبل نهاية الشهر

yajibu ʾan yaṣila ṭ-ṭalabu qabla nihāyati sh-shahr

The application must arrive before the end of the month. (Firm requirement.)

يجب علينا أن نراجع الأرقام مرة أخرى

yajibu ʿalaynā ʾan nurājiʿa l-ʾarqāma marratan ʾukhrā

We must review the figures again. (The responsible group is explicit.)

Two useful collocations with one head are يجب أن يبدأ “it must begin” and يجب على الإدارة “the administration must / is required to.” The first foregrounds the necessary event; the second foregrounds responsibility.

يجب على الموظفين إبراز بطاقاتهم عند المدخل

yajibu ʿalā l-muwaẓẓafīna ʾibrāzu biṭāqātihim ʿinda l-madkhal

Employees must show their identification cards at the entrance. (Formal rule.)

“Need not” and “must not” have different scope

English must not negates the required action; it does not merely remove the requirement. Formal Arabic makes the prohibition clear with يجب ألّا + subjunctive. For “need not / do not have to,” ليس من الضروري أن is unambiguous. Bare لا يجب أن is best avoided by learners here: logically it can deny necessity, but in contemporary use readers may also understand it as a prohibition.

ليس من الضروري أن تحضر شخصيا؛ يمكنك المشاركة عن بعد

laysa mina ḍ-ḍarūriyyi ʾan taḥḍura shakhṣiyyan; yumkinuka l-mushārakatu ʿan buʿd

You do not have to attend in person; you can participate remotely. (Absence of obligation.)

يجب ألا تفتح الباب أثناء التشغيل

yajibu ʾallā taftaḥa l-bāba ʾathnāʾa t-tashghīl

You must not open the door during operation. (Prohibition.)

ينبغي: expected or advisable, often formal

ينبغي أن is common in formal recommendations, analysis, and public guidance. It often means “should, ought to,” presenting an action as appropriate or normatively expected. It can sometimes be strong, especially in policy language, but it is not automatically identical in force to categorical يجب.

ينبغي أن نتحقق من المصدر قبل نشر الخبر

yanbaghī ʾan nataḥaqqaqa mina l-maṣdari qabla nashri l-khabar

We should verify the source before publishing the news. (Formal recommendation.)

ينبغي للمؤسسة أن توضح معايير الاختيار

yanbaghī lil-muʾassasati ʾan tuwaḍḍiḥa maʿāyīra l-ikhtiyār

The organization should clarify the selection criteria. (Formal policy style.)

In everyday instructions, من الأفضل أن “it is better to” can sound less institutional. يتعين على “it is incumbent on” is strongly (formal/bureaucratic) and useful in regulations, but inflated in a casual exchange. Spoken لازم is widespread across varieties (regional/informal); label it instead of silently mixing it into MSA.

Force in a short dialogue

قالت المديرة: يمكنكم المغادرة مبكرا اليوم، لكن يجب عليكم تسليم الملفات أولا

qālati l-mudīratu: yumkinukumu l-mughādaratu mubakkiran l-yawma, lākin yajibu ʿalaykum taslīmu l-milaffāti ʾawwalan

The director said, ‘You may leave early today, but you must submit the files first.’ (Formal workplace dialogue.)

The contrast is structural and pragmatic: يمكنكم opens an option; يجب عليكم imposes a condition. Translating both merely as “you can” would erase the difference in force.

💡

When reading a rule, locate the source of obligation, the duty-bearer, and the required event separately. Arabic may encode them as يجب + على الشخص + an أن-clause or maṣdar.

Common Mistakes

Conjugating impersonal يمكن like a personal ability verb

❌ أنا يمكن أن أحضر

Incorrect in neutral MSA—يمكن remains impersonal; express the experiencer with a suffix or لـ, or use أستطيع.

✅ يمكنني أن أحضر الاجتماع بعد الظهر

yumkinunī ʾan ʾaḥḍura l-ijtimāʿa baʿda ẓ-ẓuhr

I can attend the meeting in the afternoon.

Copying English “must for someone”

❌ يجب للطلاب أن يسجلوا اليوم

Incorrect for an imposed duty—the responsible person normally follows على, not an English-driven لـ.

✅ يجب على الطلاب أن يسجلوا اليوم

yajibu ʿalā ṭ-ṭullābi ʾan yusajjilū l-yawm

The students must register today.

Keeping indicative nūn after أنْ

❌ تستطيعين أن ترسلين الطلب الآن

Incorrect—the feminine-singular imperfect after أنْ loses its indicative nūn.

✅ تستطيعين أن ترسلي الطلب الآن

tastaṭīʿīna ʾan tursilī ṭ-ṭalaba l-ʾān

You can send the application now. (Addressed to one woman.)

Replacing a personal ability with bare impersonal possibility

❌ يمكن السباح أن يقطع المسافة في ساعة

Awkward for attributing trained ability to this swimmer; mark the person with لـ or use يستطيع.

✅ يستطيع السباح أن يقطع المسافة في ساعة

yastaṭīʿu s-sabbāḥu ʾan yaqṭaʿa l-masāfata fī sāʿa

The swimmer can cover the distance in an hour.

Leaving a regional form unlabeled

لازم الموظفين يبعتوا الأوراق اليوم

lāzim il-muwaẓẓafīn yibʿatū l-ʾawrāq il-yawm

The employees have to send the papers today. (regional: Levant; informal—not neutral MSA.)

✅ يجب على الموظفين إرسال الوثائق اليوم

yajibu ʿalā l-muwaẓẓafīna ʾirsālu l-wathāʾiqi l-yawm

Employees must send the documents today. (Formal MSA.)

Key Takeaways

أستطيع أن gives an explicit subject an ability; يمكن أن presents an event as possible.
Use يمكنني / يمكن لـ to identify the person for whom an option is available.
يجب أن states necessity; يجب على explicitly identifies who bears the duty.
Use ليس من الضروري أن for “need not,” but يجب ألّا for “must not.”
ينبغي أن is especially common for formal recommendations and norms; do not assume it always has the same force as يجب.
Every أنْ complement contains a genuinely inflected subjunctive verb.

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