In short

English negates almost everything with one word: “not”, propped up by “do”, “does” or “am”. Arabic has no all-purpose “not”. It picks a tool according to what you are negating: a present-tense verb, a verbless sentence, or a single word. This lesson gives you the three tools that cover ordinary A1 speech - لا, لَيْسَ and غَيْر - and at this level each of them has one job.

Two of them are easy. لا sits in front of a المُضارِع verb and changes nothing else: لا أَعْرِفُ. غَيْر sits in front of a single word, usually an adjective, and pulls it into the genitive: غَيْرُ مُمْكِنٍ. The third, لَيْسَ, is the interesting one. It is the negative of the verbless sentence of lesson 2, it has to be conjugated for its subject, and it puts an audible fatḥa-tanwīn on the predicate: لَسْتُ مُدَرِّسًا. That ـًا is the first case ending in this path that you can actually hear, so it is worth more attention than its size suggests.

The rule

1. لا in front of a present-tense verb. Put لا immediately before the verb. Nothing else in the sentence moves, nothing changes its ending, and there is no Arabic equivalent of the English helper “do”:

لا أَعْرِفُ. / لا يَشْرَبُ القَهْوَةَ. / لا نَسْكُنُ هُنا.

The verb keeps the same مَرْفوع ending it had in lesson 14 - the ḍamma on أَعْرِفُ, the ن on يَعْمَلونَ, تَعْمَلينَ, تَعْمَلانِ. لا is a particle (حَرْف) and particles have no endings of their own, so there is nothing to decline and nothing to agree with. One word, one slot, no side effects.

It also carries both English readings at once. لا يَعْمَلُ اليَوْمَ is equally “he does not work today” and “he is not working today”; Arabic does not separate the two.

2. لا negates only the present. لا + المُضارِع is a present-tense tool and nothing else. *لا كَتَبْتُ is not Arabic for “I did not write” - the past has its own negator (ما), and the future has another (لَنْ). Both wait for lesson 37. Until then, if the verb is not مُضارِع, do not reach for لا.

There is a second لا that also stands in front of a مُضارِع verb: the لا of prohibition, لا تَشْرَبْ “don’t drink”. You can tell them apart by the ending - the prohibitive one strips the final ḍamma - and it belongs to lesson 36. Everything on this page keeps the ḍamma.

And لا is of course also the bare word “no”: لا، شُكْرًا. That use needs no grammar.

3. لَيْسَ negates a sentence with no verb in it. A جُمْلَة اسْمِيَّة (lesson 2) has nothing for لا to attach to, so Arabic supplies a special word that behaves like a verb: لَيْسَ, “is not”. It goes at the front of the sentence:

البَيْتُ كَبيرٌ. -> لَيْسَ البَيْتُ كَبيرًا.

لَيْسَ is one of أَخَوات كانَ, “the sisters of كانَ” (lesson 43), and like كانَ it takes the old مُبْتَدَأ as its اسْم and the old خَبَر as its خَبَر. Naming them matters because the two slots now behave differently.

4. لَيْسَ must be conjugated. This is the single biggest source of learner errors. لَيْسَ is shaped like a past-tense verb and takes the past-tense person endings of lesson 18: لَسْتُ، لَسْتَ، لَسْتِ، لَيْسَ، لَيْسَتْ، لَسْنا… An unconjugated لَيْسَ with a first-person or feminine subject is simply wrong:

لَسْتُ مُدَرِّسًا. / لَسْتِ وَحْدَكِ. / لَيْسَتْ جاهِزَةً. / لَسْنا مُتَأَخِّرينَ.

When the subject is a full noun that comes after لَيْسَ, the word stays singular and agrees in gender only - the rule for any verb standing before its subject (lesson 19): لَيْسَ الطُّلّابُ جاهِزينَ، لَيْسَتِ الطّالِباتُ حاضِراتٍ. The plural forms لَيْسوا and لَسْنَ appear when no noun follows, because then the subject is inside the word itself: لَيْسوا جاهِزينَ.

5. The اسْم stays مَرْفوع; the خَبَر turns مَنْصوب. This is the whole grammatical content of لَيْسَ. The subject keeps the ḍamma it always had; the predicate swaps its ḍamma for a fatḥa:

لَيْسَ البَيْتُ (ـُ) كَبيرًا (ـًا). / لَيْسَتِ الغُرْفَةُ نَظيفَةً.

Watch the spelling of that ending. Indefinite fatḥa-tanwīn is written on a supporting alif - كَبيرًا، مُدَرِّسًا، سَهْلًا، هادِئًا - but after a final ة no alif is added and the two fatḥas simply sit on the ة itself: نَظيفَةً، جَديدَةً، مَشْغولَةً. (Words ending in ـاء, like ماءً، سَماءً، do without the extra alif too.) The sound plurals do not use a fatḥa at all: the sound masculine plural shows ـينَ (جاهِزونَ -> جاهِزينَ) and the sound feminine plural shows a kasra (حاضِراتٌ -> حاضِراتٍ). A broken plural, on the other hand, behaves like a singular and takes the ordinary fatḥa: لَيْسوا طُلّابًا.

6. This is the first ending you can hear. Case endings are invisible in ordinary writing and inaudible at a pause, which is why they feel abstract. لَيْسَ is the exception a learner meets earliest: this ending survives the pause, because the alif holds it up. Say لَسْتُ مُدَرِّسًا aloud and you really do end on a long ā - that is the pausal rule that tanwīn fatḥ is read as ā at a stop, never as -n. Say لَسْتُ مُدَرِّسٌ, which stops on a bare مُدَرِّسْ, and any Arabic speaker hears the mistake immediately - it is not a detail hidden in the vowel marks.

7. A بِـ may be added to the خَبَر. A common variant in formal writing puts a redundant بِـ in front of the predicate. The بِـ then governs it, so the word appears in the genitive rather than the accusative, and the meaning is unchanged: لَيْسَ البَيْتُ بِكَبيرٍ = لَيْسَ البَيْتُ كَبيرًا. Recognise it; you do not need to produce it.

8. A شِبْه جُمْلَة predicate is untouched. If the predicate is a preposition with its noun or a word like عِنْدَ (lesson 17), there is no single word to put in the accusative and nothing changes at all. لَيْسَ simply goes in front, and the delayed subject keeps its ḍamma:

عِنْدي وَقْتٌ. -> لَيْسَ عِنْدي وَقْتٌ. في الغُرْفَةِ طالِبٌ. -> لَيْسَ في الغُرْفَةِ طالِبٌ.

So لَيْسَ عِنْدي وَقْتًا is an error, and a frequent one: learners hear “لَيْسَ means accusative” and apply it to the wrong word. وَقْتٌ here is the subject, not the predicate.

9. غَيْر negates one word, not a sentence. غَيْر means “other than”, and it is a noun, not a particle. It forms an إِضافَة (lesson 20) with whatever follows, so the following word is مَجْرور:

غَيْرُ مُمْكِنٍ “not possible” / نَصٌّ غَيْرُ مُشَكَّلٍ “an unvocalized text” / جَوابٌ غَيْرُ صَحيحٍ “a wrong answer”.

Read it literally - “other-than-possible”, “a text other-than-vocalized” - and the genitive stops feeling arbitrary. Wherever English glues “un-”, “in-” or “non-” onto a word, Arabic usually says غَيْر.

10. غَيْر takes the case of its own slot. Because it is a noun, غَيْر declines normally while the word after it stays fixed in the genitive:

• subject / predicate slot (مَرْفوع): هٰذا غَيْرُ مُمْكِنٍ.
• after a preposition (مَجْرور): جِئْتَ في وَقْتٍ غَيْرِ مُناسِبٍ.
• object slot (مَنْصوب): قَرَأْتُ كِتابًا غَيْرَ مُفيدٍ.

Two endings sit side by side and they are not the same: غَيْرِ مُناسِبٍ, غَيْرَ مُفيدٍ. Only the second word is frozen.

One more piece: غَيْر is indefinite in form, but annexed to a definite noun it can still describe a definite one, and the phrase as a whole then reads as definite - النَّصُّ غَيْرُ المُشَكَّلِ “the unvocalized text”, الدُّوَلُ غَيْرُ العَرَبِيَّةِ “the non-Arab states”.

11. Not in this lesson. ما، لَمْ and لَنْ - the past and the future - are lesson 37. لا النّافِيَةُ لِلْجِنْس, the لا of لا مانِعَ and لا شَكَّ, is lesson 63, together with the whole system seen from above. And لَيْسَ is جامِد, “frozen”: these past-shaped forms with a present meaning are all it has - no مُضارِع, no imperative, and no past-tense form of its own, so “he was not a teacher” is ما كانَ مُدَرِّسًا (lessons 32 and 37).

Forms & patterns

لَيْسَ conjugated - learn this table

The three dual forms are left out of the table only for readability and are built the same way: أَنْتُما لَسْتُما، هُما لَيْسا (m.), هُما لَيْسَتا (f.). Note the split down the middle of the paradigm: the forms whose ending is a consonant-initial subject pronoun - ـتُ، ـتَ، ـتِ، ـتُما، ـتُمْ، ـتُنَّ، ـنا، ـنَ - lose the ـيْ (لَسْتُ، لَسْنا، لَسْنَ), and all the others keep it (لَيْسَ، لَيْسَتْ، لَيْسوا). The ـتْ of لَيْسَتْ is the feminine marker, not a subject ending, which is why that form keeps its ـيْ. This is exactly the behaviour of a hollow verb, which you meet properly in lesson 50.

لا + the present

What لَيْسَ does to the predicate

The three tools at a glance

Examples

Common mistakes

• لا أَنا مُدَرِّسٌ. -> لَسْتُ مُدَرِّسًا. - لا only negates a verb. A verbless sentence needs لَيْسَ, and لَيْسَ carries the person itself, so أَنا is not needed either.
• لَيْسَ البَيْتُ كَبيرٌ. -> لَيْسَ البَيْتُ كَبيرًا. - The اسْم keeps its ḍamma, the خَبَر takes a fatḥa. Leaving the predicate مَرْفوع is the most common لَيْسَ error of all.
• لا كَتَبْتُ الرِّسالَةَ. -> ما كَتَبْتُ الرِّسالَةَ. - لا cannot negate the past. ما can, and lesson 37 gives you it together with لَمْ and لَنْ.
• لَيْسَ الغُرْفَةُ نَظيفَةً. -> لَيْسَتِ الغُرْفَةُ نَظيفَةً. - لَيْسَ is conjugated like a past-tense verb, so a feminine subject needs لَيْسَتْ (with a kasra on the ت before الـ, to break the two silent letters apart).
• أَنا لَيْسَ طالِبًا. -> لَسْتُ طالِبًا. - Match the form to the person: لَسْتُ for “I”, لَسْتَ / لَسْتِ for “you”. لَيْسَ is the “he” form only.
• لَيْسَ عِنْدي وَقْتًا. -> لَيْسَ عِنْدي وَقْتٌ. - The predicate here is عِنْدي, a شِبْه جُمْلَة, and it cannot take an ending. وَقْتٌ is the delayed subject and stays مَرْفوع (lesson 17).
• هٰذا لا مُمْكِنٌ. -> هٰذا غَيْرُ مُمْكِنٍ. - لا does not attach to an adjective to make an opposite. Word-level negation is غَيْر.
• نَصٌّ غَيْرُ مُشَكَّلٌ. -> نَصٌّ غَيْرُ مُشَكَّلٍ. - غَيْر is the first half of an إِضافَة, so what follows it is always مَجْرور - here a kasra, never a ḍamma.
• لا يَشْرَبَ القَهْوَةَ. -> لا يَشْرَبُ القَهْوَةَ. - Negating with لا leaves the mood alone. The verb keeps the ḍamma it had in the positive sentence.
• لَيْسَ الطُّلّابُ جاهِزونَ. -> لَيْسَ الطُّلّابُ جاهِزينَ. - The sound masculine plural shows the accusative as ـينَ. There is no fatḥa to write, but the case change is still there.

Tips

• Ask one question before you negate: is there a verb? A مُضارِع verb takes لا; no verb at all takes لَيْسَ; a single word inside a bigger sentence takes غَيْر.
• Learn لَيْسَ as a chant with its predicate attached - لَسْتُ مُتْعَبًا، لَسْتَ مُتْعَبًا، لَسْتِ مُتْعَبَةً، لَيْسَ مُتْعَبًا… - so the ـًا is glued to the form from the start and never gets forgotten.
• The endings of لَيْسَ are the past-tense endings you already drilled in lesson 18 (كَتَبْتُ، كَتَبْتَ، كَتَبْنا). You are not learning a new set, only a new stem.
• Read غَيْر as “other than” rather than “not”, and the kasra behind it becomes automatic: “other than possible” is a possessive-style phrase, and those end in a kasra.
• This is one of the first places where a case ending is audible. Practise it out loud - the difference between لَسْتُ مُدَرِّسًا and لَسْتُ مُدَرِّسٌ is heard, not just written.
• Do not go looking for a مُضارِع, an imperative or a past of لَيْسَ. At this level the word covers the present verbless sentence and nothing else.
• Ignore ما، لَمْ، لَنْ for now, even if you meet them in a text. Trying to sort out four negators at once is what makes Arabic negation feel harder than it is.
• If the thing you are negating is a مُضارِع verb, لا is the tool - even when the rest of the sentence is full of nouns and adjectives: لا يَسْكُنُ في بَيْتٍ كَبيرٍ. Do not drop a لَيْسَ into the middle of a verbal sentence.