Surah Ash-Shams opens with two oaths, one straight after the other. وَٱلشَّمْسِ وَضُحَىٰهَا (wash-shamsi wa duhaha), by the sun and its morning brightness. Then وَٱلْقَمَرِ إِذَا تَلَىٰهَا (wal-qamari idha talaha), by the moon when it follows it (Ash-Shams 91:1-2).

Read those two lines aloud and something happens that most learners never notice. In the first, the ل vanishes and the ش doubles: ash-shams. In the second, the ل stays exactly where it is: al-qamar. Same two letters written on the page. Two completely different sounds.

That is the whole rule. And the Arabs named it after those two ayat: sun letters and moon letters.

What you will learn

• What the Arabic definite article ال actually does to a noun, and why it is never a separate word
• All 14 sun letters and all 14 moon letters, in full tables with a verified Quranic example for every single letter
• Two classical mnemonics that hold the whole set in your head
• How the rule plays out across Surah Al-Fatiha, ayah by ayah
• The three mistakes almost every beginner makes, including the one letter nobody expects
• An interactive checker for all 28 letters, plus a quiz to lock it in

What does the Arabic definite article ال actually do?

Arabic has one definite article and no indefinite article. Where English needs a separate little word, Arabic glues two letters onto the front of the noun and the job is done.

كِتَابٌ (kitabun) is a book. الْكِتَابُ (al-kitabu) is the book. Nothing else changed except two letters at the front and one vowel at the back.

Two things are worth pinning down before we go further.

First, ال is never written apart from its noun. There is no space. Treat it as part of the word, the way you treat the un in unhappy.

Second, ال and tanween cannot live together. The moment you attach the article, the doubled vowel at the end collapses to a single one. كِتَابٌ becomes الْكِتَابُ, never الْكِتَابٌ. This is one of the fastest reading shortcuts in the language: tanween means indefinite, ال means definite, and you will never see both on the same noun. If you want to go deeper on those endings, my guide to Arabic case endings and i’rab picks up exactly where this leaves off.

Definiteness is not a decorative detail either. It is load-bearing. In a nominal sentence the subject is normally definite and the predicate indefinite, which is precisely how you tell the two apart when you are reading, as I explain in the guide to jumla ismiyya and jumla fi’liyya.

Why does the same ال sound two different ways?

Here is the picture I keep in my head. Think of the ل as a car driving towards a gate.

Fourteen of those gates are wide open. The car drives straight through and you still see it clearly on the other side. Those are the moon letters.

The other fourteen gates are shut. The car hits the gate, merges into it, and all you hear is the gate ringing twice. Those are the sun letters.

In technical terms:

• Moon letter (لام قمرية): the ل carries a sukun and is pronounced clearly. الْقَمَر is al-qamar. Tajweed calls this izhar qamari, clear pronunciation.
• Sun letter (لام شمسية): the ل is written but not pronounced. It assimilates into the following letter, which then carries a shadda. الشَّمْس is ash-shams, not al-shams. Tajweed calls this idgham shamsi, assimilation.

And here is the part that makes life easy. In the standard Madani mushaf, the printing tells you the answer before you have to think. If the ل has a small sukun sign sitting on it, pronounce it. If the ل has no sign at all and the next letter is carrying a shadda, skip the ل and hold the next letter twice as long. The page is doing the grammar for you.

The 14 sun letters, with a Quranic example for each

With every letter in this table, the ل of the article disappears from your mouth and the letter that follows is doubled. Notice how many of these are made with the tip of the tongue near the same place the ل is made. That is not a coincidence, it is why the merge happens so naturally.

Letter	With ال	Transliteration	Meaning	Quran reference
ت	التِّين	at-tin	the fig	At-Tin 95:1
ث	الثَّمَرَات	ath-thamarat	the fruits	Al-Baqarah 2:22
د	الدِّين	ad-din	the recompense, the religion	Al-Fatiha 1:4
ذ	الذِّكْر	adh-dhikr	the reminder	Al-Hijr 15:9
ر	الرَّحْمَٰن	ar-Rahman	the Most Merciful	Al-Fatiha 1:1
ز	الزَّيْتُون	az-zaytun	the olive	At-Tin 95:1
س	السَّمَاء	as-sama	the sky	Al-Infitar 82:1
ش	الشَّمْس	ash-shams	the sun	Ash-Shams 91:1
ص	الصِّرَاط	as-sirat	the path	Al-Fatiha 1:6
ض	الضَّالِّين	ad-dallin	those who go astray	Al-Fatiha 1:7
ط	الطَّارِق	at-tariq	the night visitor	At-Tariq 86:1
ظ	الظَّالِمِين	az-zalimin	the wrongdoers	Al-Baqarah 2:35
ل	اللَّيْل	al-layl	the night	Al-Layl 92:1
ن	النَّاس	an-nas	the people	An-Nas 114:1

The 14 moon letters, with a Quranic example for each

With these, you say the ل plainly and move on. If you can read the first two ayat of Al-Fatiha, you have already produced four of them correctly.

Letter	With ال	Transliteration	Meaning	Quran reference
ا	الْإِنْسَان	al-insan	the human being	Al-Asr 103:2
ب	الْبَيْت	al-bayt	the House	Quraysh 106:3
ج	الْجَنَّة	al-jannah	the garden, Paradise	Al-Baqarah 2:35
ح	الْحَمْد	al-hamd	the praise	Al-Fatiha 1:2
خ	الْخَنَّاس	al-khannas	the retreating whisperer	An-Nas 114:4
ع	الْعَالَمِين	al-alamin	all the worlds	Al-Fatiha 1:2
غ	الْغَفُور	al-Ghafur	the Most Forgiving	Al-Buruj 85:14
ف	الْفَلَق	al-falaq	the daybreak	Al-Falaq 113:1
ق	الْقَمَر	al-qamar	the moon	Ash-Shams 91:2
ك	الْكِتَاب	al-kitab	the Book	Al-Baqarah 2:2
م	الْمُسْتَقِيم	al-mustaqim	the straight	Al-Fatiha 1:6
ه	الْهُدَىٰ	al-huda	the guidance	Al-Baqarah 2:159
و	الْوَسْوَاس	al-waswas	the whisperer	An-Nas 114:4
ي	الْيَوْم	al-yawm	the day	Al-Maidah 5:3

If any of those letters are still shaky on the tongue, go back to the Arabic alphabet pronunciation guide for all 28 letters first. This rule is only as good as your grip on the letters it operates on.

Two mnemonics that hold all 28 letters

Arabic teachers have passed these two phrases down for centuries, and they work because every word begins with one of the letters in the set. Memorise one side and the other side is simply everything else.

The moon letters: ابْغِ حَجَّكَ وَخَفْ عَقِيمَهُ (ibghi hajjaka wa khaf aqimah). The first letters spell out ا ب غ ح ج ك و خ ف ع ق ي م ه, all fourteen moon letters.

The sun letters: طِبْ ثُمَّ صِلْ رَحِمًا تَفُزْ ضِفْ ذَا نِعَمْ، دَعْ سُوءَ ظَنٍّ زُرْ شَرِيفًا لِلْكَرَمْ (tib thumma sil rahiman tafuz, dif dha niam, da su a zannin zur sharifan lil-karam). The first letters spell out ط ث ص ر ت ض ذ ن د س ظ ز ش ل, all fourteen sun letters.

My honest advice: only bother with the moon one. It is short, it is easy to say, and it does the whole job. Fourteen letters in, and if the letter in front of you is not on that list, it is a sun letter. That is the entire decision.

How does the rule play out across Surah Al-Fatiha?

You already recite this surah at least seventeen times a day. It happens to contain both categories, several times over, in seven short ayat. Walk through it once with this rule switched on and you will never read it the same way again.

Ayah	Word	First letter after ال	Sun or moon	You say
1:1	الرَّحْمَٰنِ	ر	Sun	ar-Rahman
1:1	الرَّحِيمِ	ر	Sun	ar-Rahim
1:2	الْحَمْدُ	ح	Moon	al-hamdu
1:2	الْعَالَمِينَ	ع	Moon	al-alamin
1:4	الدِّينِ	د	Sun	ad-din
1:6	الصِّرَاطَ	ص	Sun	as-sirat
1:6	الْمُسْتَقِيمَ	م	Moon	al-mustaqim
1:7	الضَّالِّينَ	ض	Sun	ad-dallin

Ayah 1:6 is the one to sit with. ٱهْدِنَا ٱلصِّرَٰطَ ٱلْمُسْتَقِيمَ, ihdina as-sirat al-mustaqim. Two nouns side by side, both carrying the same article, and the article behaves differently on each one. Sun, then moon, in the space of a single breath. If you can hear the difference in that one ayah, you have the rule.

The three mistakes almost everyone makes

1. Assuming ل must be a moon letter

This one catches nearly everybody, and the logic behind the error is understandable. The article itself is a ل, so surely a ل cannot swallow another ل? It can, and it does. ل is a sun letter.

اللَّيْل is not a casual al-layl tossed off in one beat. It is al-layl with a genuinely doubled ل that you hold, because the article has merged into the root letter. Open Surah Al-Layl and look at the very first word of 92:1: the shadda is sitting right there on the ل, telling you to lean on it. The tell is always the shadda, never your intuition.

2. Pronouncing the hamza of ال in the middle of a phrase

The alif at the front of ال carries hamzat al-wasl, a connecting hamza. You pronounce it only when you begin speech there. Mid-flow, it drops out completely and the previous vowel runs straight into the ل.

So Al-Fatiha 1:2 is al-hamdu lillahi rabbil-alamin. Not rabbi al-alamin. And Ash-Shams 91:1, which opens with the particle وَ, is wash-shamsi, not wa ash-shamsi. Once you start listening for this in recitation you will hear it everywhere.

The same elision happens after a preposition. بِالْحَقِّ is bil-haqq, and after لِ the alif of the article is dropped in writing altogether: لِلنَّاسِ, lin-nas. If prepositions are new territory, the guide to harf al-jarr and the Arabic prepositions covers how each one behaves.

3. Leaving tanween on a noun that already has ال

Writing الْكِتَابٌ is like writing the a book. Pick one. The article and the tanween are two ways of doing opposite jobs, and Arabic will not let you stack them.

A related trap: when a demonstrative points at a noun, the noun keeps its article. هَٰذَا الْكِتَابُ means this book, with ال intact on كِتَاب. Drop the article and the meaning shifts entirely. The post on Arabic demonstrative pronouns works through why.

Interactive: check any Arabic letter against the ال rule

Tap a letter to see what happens when the definite article lands in front of it, with a verified Quranic word for each one. Filter by category if you are drilling one half at a time.

Test yourself: sun and moon letters quiz

Six questions on exactly what we covered. Answer each one and you will get the reasoning straight away, not just a tick or a cross. If you want to test the letters themselves rather than the rule, the Arabic alphabet and makharij quiz is the companion to this one.

Try it for 60 seconds before you close this tab

Open Surah An-Nas. It is six short ayat, and four of its nouns carry the article: النَّاس, الْوَسْوَاس, الْخَنَّاس, الْجِنَّة.

Say each one out loud and label it sun or moon before you check. Then check. النَّاس is sun, so an-nas with a held ن. The other three are all moon letters, so the ل is clear in each: al-waswas, al-khannas, al-jinnah. One surah, both categories, sixty seconds.

Do that with one short surah a day for a fortnight and this stops being a rule you recall and becomes a sound you expect. That is the point at which grammar starts paying you back.

Where this fits in the bigger picture

Sun and moon letters sit in an unusual spot. They are grammar, because ال is the definite article and definiteness drives half of Arabic syntax. They are also tajweed, because the whole rule is about assimilation in the mouth. Learning them once pays into both accounts, which is why I put them early in any beginner sequence.

Next steps, in the order I would take them: get the article solid, then the seven core patterns in the Arabic grammar guide covering 7 essential rules, then build the vocabulary to actually use them with the 20 most frequent Quranic words. If you would rather see the whole path laid out at once, the complete roadmap for learning Quranic Arabic maps it end to end.

You can also grab the free PDF of the 50 most common Quranic root words. Almost every noun on that sheet will show up wearing ال at some point, so it doubles as practice material for exactly what you have just learned.

And if you want this taught in sequence with daily structure rather than picked up post by post, that is what the 28-Day Quranic Arabic Course is for. It is $37 (was $77) and comes with a 7-day money-back guarantee. Twenty-eight days will not make you fluent, and I would not trust anyone who told you otherwise. What it will do is get you reading short surahs and recognising what the words are doing, which is a real and reachable goal.

Frequently asked questions

What are sun and moon letters in Arabic?

They are the two halves of the Arabic alphabet, split by how they react to the definite article ال. After the article, the 14 sun letters absorb the ل and double themselves, so الشَّمْس is read ash-shams. The 14 moon letters leave the ل audible, so الْقَمَر is read al-qamar. The spelling never changes, only the pronunciation.

Why are they called sun and moon letters?

They are named after the two model words. الشَّمْس (the sun) begins with ش, which absorbs the ل, so every letter that behaves that way is called a sun letter. الْقَمَر (the moon) begins with ق, which lets the ل through, so those are moon letters. Both words appear in consecutive ayat at Ash-Shams 91:1-2.

Is ل a sun letter or a moon letter?

ل is a sun letter, which surprises most beginners. In اللَّيْل the ل of the article merges into the root ل and you hold a doubled sound: al-layl. Look for the shadda on the second ل and the mushaf will confirm it for you.

Does the sun and moon rule change the meaning of a word?

No. It is purely a pronunciation rule. The meaning change comes from the article itself, which turns an indefinite noun into a definite one. Whether the ل is heard or absorbed does not alter what the word means, though mispronouncing it in recitation is still something to correct.

Do I have to memorise all 28 letters to use this rule?

You only need one half. Memorise the 14 moon letters using the phrase ابْغِ حَجَّكَ وَخَفْ عَقِيمَهُ and treat every other letter as a sun letter. In practice most people stop consulting the list within a few weeks, because a vowelled mushaf marks the answer on the page with either a sukun or a shadda.

Is this grammar or tajweed?

Both, which is part of why it is worth learning early. Grammarians treat ال as the marker of definiteness, and tajweed treats the sun letter merge as idgham shamsi and the moon letter as izhar qamari. One rule, two disciplines, and you get both for the price of one afternoon.

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Written by Hesham (H's Qalam), UK medical doctor and Quranic Arabic teacher, creator of the 28-Day Quranic Arabic Course.