In short

English marks when and where with prepositions: in the morning, at night, in front of the house. Arabic can do that too - في الصَّباحِ is perfectly good - but its own everyday answer is a case ending. You take the noun that names the time or the place and put it in the accusative: صَباحًا “in the morning”, لَيْلًا “at night”, أَمامَ البَيْتِ “in front of the house”. Nothing is written in front of it and nothing is spoken. The old grammarians’ name for such a word says exactly why: المَفْعولُ فيهِ, “the thing the action was done in” - the في is inside the word, in its ending.

The workload here is small and the payoff is immediate, because these are the words you need in every sentence about a day, a place or a habit. There are two endings to control: the fatḥa on the adverbial itself, and - for the place words - the kasra on the noun right after it, because أَمامَ، تَحْتَ، بَعْدَ and their kind are normally the first term of an إِضافَة. Add one spelling rule about where the little alif of the tanwīn goes, and you can say when, where and how.

The rule

1. A ظَرْف is a noun doing an adverb’s job. صَباحٌ is “a morning”, a perfectly ordinary noun. Put it in the accusative and it stops naming a thing and starts naming a time: صَباحًا “in the morning”. Nothing else changes - no particle, no article. This is why lesson 16 warned you that عِنْدَ، مَعَ، قَبْلَ، بَعْدَ are not really حُروفُ جَرّ: a preposition is a حَرْف and has no case at all, while these are أَسْماء that normally sit in the accusative. A ظَرْف answers one of two questions: مَتى؟ (when) or أَيْنَ؟ (where).

2. Time: an indefinite noun with tanwīn-fatḥa. The core set is short and worth memorising as a block: صَباحًا، مَساءً، لَيْلًا، نَهارًا، ظُهْرًا، غَدًا، أَحْيانًا، دائِمًا، أَبَدًا. The same accusative also measures a stretch of time: اِنْتَظَرْتُ ساعَةً “I waited an hour”, دَرَسَ سَنَةً “he studied for a year”. Two practical notes:

• في + a definite time noun is an equally correct alternative, not a mistake: صَباحًا and في الصَّباحِ both work, and في المَساءِ is as common as مَساءً. What you must not do is use both at once.
• أَبَدًا needs a negative to mean “never”: لا أُدَخِّنُ أَبَدًا “I never smoke”. On its own it does not carry the negation.

3. The definite type - and two frozen time words. Most time adverbials are indefinite, but a handful are definite and accusative anyway. اليَوْمَ “today” and اللَّيْلَةَ “tonight” carry الـ and still take the fatḥa, because they are still adverbs: اليَوْمَ وَصَلَ الضَّيْفُ. Compare اليَوْمُ جَميلٌ “the day is beautiful” - there the word is the subject of a sentence, so it is مَرْفوع. الآنَ “now” always ends in a fatḥa and never moves. أَمْسِ “yesterday” is مَبْنِيّ: used as an adverb it is frozen with a kasra wherever it stands in the sentence, so there is no *أَمْسًا and no *أَمْسَ - just أَمْسِ. Finally, you can build a definite time phrase as an إِضافَة with the first word in the accusative: يَوْمَ الجُمُعَةِ “on Friday”, صَباحَ الغَدِ “tomorrow morning”, مَساءَ السَّبْتِ “on Saturday evening”.

4. Place and relation words: fatḥa on the ظَرْف, kasra on the noun after it. This is the single most useful rule in the lesson. The relational words أَمامَ، خَلْفَ، وَراءَ، فَوْقَ، تَحْتَ، بَيْنَ، عِنْدَ، حَوْلَ، داخِلَ، خارِجَ، قَبْلَ، بَعْدَ، خِلالَ، أَثْناءَ do two things at once:

• they stand in the accusative, so their own ending is a bare fatḥa - the one thing that can change it is a preposition in front, see point 6;
• they are the first term of an إِضافَة, so everything lesson 20 said applies to them - no الـ, no tanwīn, and the following noun is مَجْرور.

أَمامَ البَيْتِ، خَلْفَ المَدْرَسَةِ، فَوْقَ الطّاوِلَةِ، تَحْتَ السَّريرِ، عِنْدَ البابِ، حَوْلَ المَدينَةِ، قَبْلَ الظُّهْرِ، بَعْدَ الدَّرْسِ، خِلالَ الأُسْبوعِ، أَثْناءَ الرِّحْلَةِ. Two vowels, always the same shape: -a … -i. Say them as one unit until the pair is automatic.

بَيْنَ needs two things to sit between, so it is followed by a dual, a plural, or two nouns joined by و: بَيْنَ الطّالِبَيْنِ، بَيْنَ الطُّلّابِ، بَيْنَ البَيْتِ وَالمَدْرَسَةِ. The dual after it is genitive, so it ends in ـَيْنِ, never ـانِ.

5. With a pronoun, the same words take the attached set. Because the ظَرْف is a مُضاف, the pronoun that follows is an ordinary مُضافٌ إِلَيْهِ, exactly as in كِتابُهُ: أَمامَهُ “in front of him”, عِنْدَنا “at our place / we have”, بَعْدَكَ “after you”, بَيْنَهُما “between the two of them”, حَوْلي “around me”. Only the first-person ي replaces the fatḥa: أَمامي، عِنْدي، بَعْدي.

6. Do not put في in front of the place words. The في is already inside the word, so *في أَمامِ البَيْتِ is a double preposition and one of the loudest learner errors there is. Say أَمامَ البَيْتِ.

There is a real exception, and it is worth knowing because you will read it: after مِنْ or إِلى these words behave like ordinary nouns and go genitive - مِنْ أَمامِ البَيْتِ “from in front of the house”, مِنْ تَحْتِ الطّاوِلَةِ “from under the table”, مِنْ عِنْدِهِ “from his place”, إِلى جانِبِ النَّهْرِ “to the side of the river”. The everyday word for “next to” is exactly this type: بِجانِبِ البَيْتِ, with بِـ and a kasra. So the test is simple - a preposition in front means genitive, nothing in front means accusative.

One word in the list is fully at home both ways: أَثْناءَ الرِّحْلَةِ and في أَثْناءِ الرِّحْلَةِ are both standard MSA, so do not “correct” the في version when you meet it.

7. قَبْلُ and بَعْدُ standing alone. When the second term is dropped but still understood, these two freeze with a ḍamma: رَأَيْتُهُ مِنْ قَبْلُ “I saw him before”, وَصَلْنا مِنْ بَعْدُ “we arrived afterwards”. This is a fixed idiom, not a case you have to compute; learn the two phrases as vocabulary. With a following noun they are back to normal: قَبْلَ الظُّهْرِ.

8. Manner rides on the same accusative. How something is done uses the very same ending: سَريعًا “quickly”, جَيِّدًا “well”, كَثيرًا “a lot”, قَليلًا “a little”, تَقْريبًا “approximately”, مَعًا “together”, أَيْضًا “also”. Note that Arabic does not make these agree with anything - they are not adjectives here, so *يَتَكَلَّمُ جَيِّدٌ is wrong the way English “he speaks good” is wrong.

Many of them have a twin built from بِـ + a verbal noun in the genitive: بِسُرْعَةٍ، بِهُدوءٍ، بِسُهولَةٍ، بِشَكْلٍ جَيِّدٍ. Both are fully standard. سَريعًا and بِسُرْعَةٍ are interchangeable; for “quietly” and “easily” the بِـ phrase is the ordinary idiom - you will rarely if ever meet a bare accusative in that sense. When in doubt, بِـ + noun is the safe road.

A footnote for later: when the accusative describes the state of a person rather than the manner of an action - “he came back tired”, “she left smiling” - that is الحال, a related but separate construction with its own agreement rules. It is lesson 55, and you do not need it yet.

9. Where the alif of the tanwīn sits. The tanwīn-fatḥa is normally propped up by an alif that you write but never read as a syllable of its own: سَريعًا، كِتابًا، شُكْرًا، صَباحًا. Two endings refuse that alif:

• a word ending in ة takes the tanwīn on the ة itself: سَنَةً، لَيْلَةً، مَرَّةً - never *سَنَةاً;
• a word ending in a hamza that already sits after a long alif takes it on the hamza: مَساءً، ماءً، هَواءً. Writing *مَساءاً is a spelling error, not a variant - you would be putting two alifs in a row.

A hamza that is not after a long alif keeps the prop as usual: شَيْئًا، جُزْءًا، بُطْئًا.

10. This is the one ending you can hear. The pronunciation guide taught the pausal form: at the end of an utterance the endings ـُ and ـِ are simply dropped. The adverbial ـً is not - it survives as a long ā. That is why شُكْرًا and جَيِّدًا keep a clear long vowel at the end even from speakers who pronounce no other case ending. Practically: this one ending is worth saying out loud always.

11. Position is free, and a ظَرْف can be the whole predicate. The adverbial may follow the verb (سافَرْتُ صَباحًا) or open the sentence for emphasis (صَباحًا سافَرْتُ). And a place phrase can serve as the خَبَر of a nominal sentence all by itself, exactly like a في phrase in lesson 17: المِفْتاحُ تَحْتَ السَّريرِ، الحَديقَةُ خَلْفَ البَيْتِ.

What this lesson does not cover: joining a whole clause to a time word - عِنْدَما وَصَلَ، بَعْدَ أَنْ أَكَلَ - which is lesson 38, and the accusative that repeats the verb’s own verbal noun for emphasis, which is lesson 60.

Forms & patterns

Time - indefinite noun in the accusative (ظُروفُ الزَّمان):

Time words that do not follow that shape:

Place and relation - fatḥa on the ظَرْف, kasra on the noun after it (ظُروفُ المَكان):

The same words with an attached pronoun (only ي displaces the fatḥa):

The dual and feminine plural rows (ـكُما، ـهُما، ـكُنَّ، ـهُنَّ) work exactly as in lesson 7 and are left out here.

Manner: the accusative and its بِـ twin:

Where the tanwīn-fatḥa sits:

Examples

Common mistakes

• أَمامُ البَيْتِ -> أَمامَ البَيْتِ - with nothing in front of it the ظَرْف stays in the accusative. Its ending is a fatḥa whatever the verb around it is doing; only a preposition before it (مِنْ أَمامِ البَيْتِ) makes it genitive.
• أَمامَ البَيْتُ -> أَمامَ البَيْتِ - and the noun after it is genitive, because the ظَرْف is the first term of an إِضافَة. The pattern is always -a … -i.
• في أَمامِ البَيْتِ -> أَمامَ البَيْتِ - no preposition in front. The في is already built into the adverbial; that is literally what المَفْعولُ فيهِ means.
• أَمامًا البَيْتِ -> أَمامَ البَيْتِ - a مُضاف takes no tanwīn and no الـ, so *الأَمامَ البَيْتِ is wrong for the same reason.
• يَتَكَلَّمُ جَيِّدٌ -> يَتَكَلَّمُ جَيِّدًا - a manner word is accusative, not a nominative adjective agreeing with the subject.
• مَساءاً -> مَساءً - a final hamza after a long alif carries the tanwīn itself; adding a prop alif would give you two alifs in a row.
• سَنَةاً -> سَنَةً - the same for a word ending in ة. The prop alif is only for words that end in a plain consonant.
• أَمْسًا -> أَمْسِ - أَمْسِ is مَبْنِيّ: one frozen form with a kasra, no case ending and no tanwīn to add.
• اليَوْمُ وَصَلَ الضَّيْفُ -> اليَوْمَ وَصَلَ الضَّيْفُ - اليَوْمَ is definite but still an adverb here, so it is accusative. The ḍamma would make it the subject: اليَوْمُ جَميلٌ.
• بَيْنَ الطّالِبانِ -> بَيْنَ الطّالِبَيْنِ - after بَيْنَ the dual is genitive, so it ends in ـَيْنِ. Nominative ـانِ cannot appear as a مُضافٌ إِلَيْهِ.

Tips

• Drill the place words as a two-vowel chant, never as single words: أَمامَ البَيْتِ، تَحْتَ السَّريرِ، بَعْدَ الدَّرْسِ. The pair of endings is the grammar; the meaning is just vocabulary.
• A quick self-test for any adverbial you are unsure of: could English put “in” or “at” in front of it? If yes, Arabic puts nothing in front and a fatḥa at the end.
• When you cannot recall whether a manner word exists in the accusative, fall back on بِـ + noun in the genitive: بِسُرْعَةٍ، بِهُدوءٍ، بِسُهولَةٍ. It is never wrong, and it is what most writing uses anyway.
• Watch the ending after بِـ: it is a preposition, so بِسُرْعَةٍ with a kasra - never *بِسُرْعَةً.
• Store اليَوْمَ، الآنَ، أَمْسِ as three separate irregular items rather than trying to derive them. Everything else in the time set is regular.
• Say the ـً out loud even in isolated words. It is the only case ending that survives the pausal form, so شُكْرًا، جَيِّدًا، سَريعًا all end in a clear long vowel when careful speakers say them.
• In unvocalized text the place words are still recognisable: أمام البيت has no ال and no linking word, which is the visual signature of a construct. Read it as ظَرْف + genitive.
• Do not reach yet for عِنْدَما or بَعْدَ أَنْ. As long as what follows is a noun, this lesson covers you; a following verb is lesson 38.