In short

Cardinal numbers say how many; ordinals say which one in the row - the third lesson, the fifth floor, the first time. Grammatically the Arabic ordinal is not a number at all. It is an ordinary adjective cut on the pattern فاعِل, and it behaves exactly like كَبير or جَديد: it follows its noun and it agrees with it. The same handful of roots also yields the fractions (نِصْف، ثُلُث، رُبُع), and the clock and the date are built almost entirely out of ordinals, which is why all four topics live in one lesson.

After the counting rules of lesson 26 this comes as a relief: no reverse gender agreement, no genitive plural to keep track of, nothing to invert. What you actually have to memorize is small

• two ordinals that are irregular (أَوَّل and ثانٍ), one root that hides its د (سادِس, not anything built on the ت of سِتَّة), and four or five fixed frames for telling the time. Then you can say when the meeting is, when you were born, and how much of the book you have read.

The rule

1. Ordinals 1-10 are cut on فاعِل. Take the cardinal’s root and pour it into the shape فاعِل: ثَلاثَةٌ -> ثالِثٌ، خَمْسَةٌ -> خامِسٌ، سَبْعَةٌ -> سابِعٌ، عَشَرَةٌ -> عاشِرٌ. The feminine is made the ordinary way, by adding ة: ثالِثَةٌ، خامِسَةٌ، عاشِرَةٌ. Two entries do not follow the rule and must be learned as vocabulary: “first” is أَوَّلُ / أُولى (no فاعِل anywhere in it), and “second” is ثانٍ / ثانِيَةٌ, which is regular in shape but irregular in its endings (rule 4).

2. سادِس, and why it has a د. The cardinal سِتَّةٌ looks as if its ordinal should be built on س-ت-ت, but the root is really س-د-س; the د assimilated long ago inside سِتَّة and it comes back in every other word of the family - the fraction سُدُسٌ, the adjective سُداسِيٌّ (six-part). So the ordinal is سادِسٌ / سادِسَةٌ. Learn سِتَّة and سادِس as a pair and the problem disappears.

3. An ordinal is an ordinary نَعْت, so it agrees three ways. Gender, case and definiteness - exactly the agreement of lesson 8, and it comes after its noun, where English puts it before:

• الدَّرْسُ الثّالِثُ - the third lesson (masculine, nominative, definite)
• الصَّفْحَةُ الثّالِثَةُ - the third page (feminine)
• في الفَصْلِ الأَوَّلِ - in the first chapter (genitive after في, so both words end in a kasra)
• قَرَأْتُ الفَصْلَ الأَوَّلَ - I read the first chapter (accusative)

Definiteness is the rule learners break most: if the noun has الـ, the ordinal must have الـ too. الدَّرْسُ الثّالِثُ is “the third lesson”; الدَّرْسُ ثالِثٌ is a complete sentence, “the lesson is a third one”. An indefinite pair is possible and means what it says: دَرْسٌ ثالِثٌ, “a third lesson”.

4. ثانٍ is an اسْم مَنْقوص - a noun that ends in a weak ي. Its endings behave unusually and this is worth getting right early, because “second” is everywhere:

• indefinite nominative and genitive: ثانٍ (the ي disappears from the writing entirely)
• indefinite accusative: ثانِياً (the ي comes back)
• definite: الثّاني in the nominative and the genitive - the ending is there but silent (مُقَدَّرَة, “estimated”), so nothing is written on the ي - and الثّانِيَ in the accusative

So: جاءَ طالِبٌ ثانٍ، رَأَيْتُ طالِباً ثانِياً، الطّالِبُ الثّاني، رَأَيْتُ الطّالِبَ الثّانِيَ. The feminine ثانِيَةٌ / الثّانِيَةُ is completely regular and is the form you will use most, because it is the one the clock uses. Why the ي behaves like this is the subject of lesson 41; for now copy the four forms.

5. أَوَّل refuses tanwīn. أَوَّلُ is a diptote (مَمْنوعٌ مِنَ الصَّرْف): when it is indefinite and standing on its own it takes no tanwīn at all, and its genitive is a fatḥa, not a kasra. In practice you meet it in two safe positions where the problem never arises - with الـ (الفَصْلُ الأَوَّلُ، في الفَصْلِ الأَوَّلِ) and as the first word of an إِضافَة (أَوَّلُ مَرَّةٍ، لِأَوَّلِ مَرَّةٍ), because both of those restore the ordinary kasra. The feminine أُولى / الأُولى never changes its ending at all: المَرَّةُ الأُولى، في المَرَّةِ الأُولى. One fixed form is worth memorizing separately: the adverb أَوَّلاً, “first of all, firstly”, which does carry tanwīn.

6. The ordinal can come first, as an إِضافَة. Beside الدَّرْسُ الثّالِثُ, Arabic can say ثالِثُ دَرْسٍ - the ordinal in front, normally masculine even when the noun is feminine, and the noun singular, indefinite and genitive behind it (lesson 20). The meaning is the same but the phrasing is tighter, and with أَوَّل and آخِر it is the normal way to speak: أَوَّلُ يَوْمٍ (the first day)، أَوَّلُ مَرَّةٍ (the first time)، آخِرُ قِطارٍ (the last train)، ثالِثُ طابِقٍ.

7. 11 and 12 are frozen. From eleven to nineteen the ordinal is a compound, and like the cardinal compounds of lesson 26 both halves are locked on a fatḥa and never change for case: الحادِيَ عَشَرَ (m) / الحادِيَةَ عَشْرَةَ (f)، الثّانِيَ عَشَرَ (m) / الثّانِيَةَ عَشْرَةَ (f). Note that “eleventh” is الحادي, not الأَحَد. From twenty on, the tens serve as ordinals unchanged (الذِّكْرى العِشْرونَ), and the units are joined in front with وَ: الدَّرْسُ الثّالِثُ وَالعِشْرونَ، القَرْنُ الحادي وَالعِشْرونَ.

8. Fractions are cut on فُعُل. ثُلُثٌ (a third)، رُبُعٌ (a quarter)، خُمُسٌ (a fifth)، سُدُسٌ (a sixth)، ثُمُنٌ (an eighth). Every one of these is equally correct with a sukūn on the middle letter - ثُلْثٌ، رُبْعٌ، خُمْسٌ - and that is the pronunciation you will hear on the clock. “Half” is outside the pattern: نِصْفٌ. The plurals are broken plurals on أَفْعال: أَنْصافٌ، أَثْلاثٌ، أَرْباعٌ، أَخْماسٌ، أَثْمانٌ. To build a compound fraction, count the plural with the rules you already know: ثَلاثَةُ أَرْباعٍ (three quarters)، خَمْسَةُ أَثْمانٍ (five eighths). Two thirds is a dual: ثُلُثانِ, and in an إِضافَة it drops its ن - ثُلُثا الطُّلّابِ. A fraction of something specific is simply an إِضافَة: نِصْفُ الكِتابِ، رُبْعُ السّاعَةِ. Percentages are said with في المِئَةِ (or بِالمِئَةِ): عِشْرونَ في المِئَةِ.

9. The clock runs on feminine ordinals. The frame is السّاعَةُ + a feminine ordinal; the ordinal is feminine because it is agreeing with السّاعَة, which is itself the noun in the phrase: السّاعَةُ الثّالِثَةُ, literally “the hour is the third one”. One o’clock breaks the series - السّاعَةُ الواحِدَةُ, not الأُولى. Minutes are added with وَ and subtracted with إِلّا:

• السّاعَةُ الثّالِثَةُ وَالرُّبْعُ / وَالنِّصْفُ / وَعَشْرُ دَقائِقَ
• السّاعَةُ الرّابِعَةُ إِلّا رُبْعاً / إِلّا عَشْرَ دَقائِقَ

Two case rules keep this tidy. What follows وَ copies the case of السّاعَة, so it changes when a preposition arrives: السّاعَةُ الثّامِنَةُ وَالنِّصْفُ but في السّاعَةِ الثّامِنَةِ وَالنِّصْفِ. What follows إِلّا is accusative and stays accusative in every position: إِلّا رُبْعاً. (إِلّا is the whole subject of lesson 62; here take the accusative as part of the frame.) Note also that دَقيقَة is feminine, so its numbers behave in reverse as usual - خَمْسُ دَقائِقَ، عَشْرُ دَقائِقَ with no ة on the number. The question is كَمِ السّاعَةُ؟ and the time of day is an accusative adverb: صَباحاً، ظُهْراً، مَساءً، لَيْلاً، or بَعْدَ الظُّهْرِ.

10. Dates: days, months, years. The days are أَيّامُ الأُسْبوعِ, all of them definite and mostly built on numbers themselves - الأَحَد is “the one”, الاثْنَيْن “the two”, الثُّلاثاء “the three”. The working week in much of the Arab world runs مِنَ الأَحَدِ إِلى الخَميسِ. For the months there are two competing sets: the international names (يَنايِر، فِبْرايِر، مارِس …) are standard in Egypt, Sudan, Yemen and the Gulf, while Syria, Lebanon, Jordan, Palestine and Iraq use the old Semitic set (كانونُ الثّاني، شُباط، آذار …) - the same month, a different word, and note that four of those names contain the ordinals الأَوَّل and الثّاني. The Maghreb goes its own way again: Algeria and Tunisia print French-derived names (جانْفي، فيفْري …). Month names are foreign or frozen proper nouns: they take no tanwīn, and most of them show a fatḥa in the genitive (في سِبْتَمْبَرَ), while the ones ending in a long vowel never change (في مايو).

A date is written in figures and read day-month-year: 3 مارِس 2026. (This course writes the figures 0-9; much of the Mashriq prints the Arabic-Indic shapes instead, and reads them the same way.) Two frames cover almost everything you need: the ordinal one, وَصَلَ في الأَوَّلِ مِنْ سِبْتَمْبَرَ, and the year frame, وُلِدَ عامَ 1998 (with عامَ in the accusative as an adverb of time) or وُلِدَ في عامِ 1998 (with في, so genitive). وُلِدَ is a passive verb - lesson 52 - so take it as a phrase for now. The year itself is an ordinary cardinal when you say it out loud, and after عامِ it stands in the genitive: في عامِ أَلْفٍ وَتِسْعِمِئَةٍ وَثَمانِيَةٍ وَتِسْعينَ.

Forms & patterns

The ordinals 1-12, with the cardinal they come from:

The endings of ثانٍ, the one ordinal whose case marks are irregular:

The fractions (the sukūn variants ثُلْث، رُبْع، خُمْس are equally correct):

Telling the time - one hour, all the usual slices:

The days of the week:

The two month sets, side by side (both are Modern Standard Arabic - the split is regional):

Examples

Common mistakes

• السّاعَةُ الثَّلاثَةُ -> السّاعَةُ الثّالِثَةُ - the clock takes the ordinal, never the cardinal. الثَّلاثَة is the quantity “three”, الثّالِثَة is “the third one”.
• السّاعَةُ الأُولى -> السّاعَةُ الواحِدَةُ - one o’clock is the single slot where the clock uses واحِدَة. الأُولى means “the first” and is used of chapters, rooms and times, not of the hour on the dial.
• الدَّرْسُ ثالِثٌ -> الدَّرْسُ الثّالِثُ - the ordinal is a نَعْت and must copy the definiteness of its noun. Left indefinite it turns the phrase into a sentence: “the lesson is a third one”.
• الصَّفْحَةُ الثّالِثُ -> الصَّفْحَةُ الثّالِثَةُ - and it must copy the gender. صَفْحَة is feminine, so the ordinal takes ة.
• في الفَصْلِ الأَوَّلُ -> في الفَصْلِ الأَوَّلِ - and the case. After في both words are مَجْرور; the ordinal is not exempt because it is a number.
• الطّالِبُ الثّانِيْ -> الطّالِبُ الثّاني - never put a sukūn on the ي of الثّاني. Its nominative and genitive endings are silent, and the ي is simply left bare; only the accusative is written, الثّانِيَ.
• الفَصْلُ السّائِتُ -> الفَصْلُ السّادِسُ - the ordinal of سِتَّة is built on the root س-د-س, which also gives the fraction سُدُس. There is no ت in it.
• الدَّرْسُ الأَحَدَ عَشَرَ -> الدَّرْسُ الحادِيَ عَشَرَ - eleventh is الحادي, not the cardinal أَحَد. The second half عَشَرَ never changes.
• السّاعَةُ الرّابِعَةُ إِلّا رُبْعٌ -> السّاعَةُ الرّابِعَةُ إِلّا رُبْعاً - whatever follows إِلّا is accusative, in every position in the sentence.
• في السّاعَةِ الثّامِنَةِ وَالنِّصْفُ -> في السّاعَةِ الثّامِنَةِ وَالنِّصْفِ - what follows وَ copies the case of السّاعَة, so it turns to a kasra after a preposition.

Tips

• Learn the ordinal as a shape, not as twelve separate words: take the cardinal, keep its three letters, pour them into فاعِل. Only 1, 2 and 6 have to be memorized on their own.
• Say the time out loud in Arabic every time you check a clock for a week. Four frames (وَالرُّبْعُ، وَالنِّصْفُ، إِلّا رُبْعاً، وَعَشْرُ دَقائِقَ) cover nearly every hour of the day.
• Memory hook for سادِس: the fraction سُدُس shows you the د that سِتَّة swallowed.
• When you are unsure of the ending of a clock phrase, ask what case السّاعَة is in. Everything joined with وَ follows it; only the piece after إِلّا refuses and stays accusative.
• Learn the month set of the region you actually read or travel in, and keep the other for recognition. A news wire will use كانونُ الثّاني and يَنايِر for the same month on the same day.
• Digits stay digits on the page - 3 مارِس 2026 - and only become words when you speak. Do not try to inflect the figure you have written.
• Two forms are worth over-learning because they appear on every form you will ever fill in: تاريخُ الميلادِ (date of birth) and رَقْمُ الصَّفْحَةِ (page number).
• Leave the theory alone for now: why ثانٍ drops its ي and why أَوَّلُ refuses tanwīn is lesson 41, and the grammar of إِلّا is lesson 62. The forms above work without either.