ʾIʿrab
Etymology. The term literally means 'making [the word] Arabic'. It is the stem IV "masdar" of the root ‘-r-b (), meaning "to be fluent", so means "making a thing expressed, disclosed or eloquent". The term is cognate to the word "Arab" itself. Grammatical cases. Case is not shown in standard orthography, with the exception of indefinite accusative nouns ending in any letter but "" () or "" followed by "" (), where the "" "sits" on the letter before an alif added at the end of the word (the alif shows up even in unvowelled texts). Cases, however, are marked in the Qur'an, children's  books, and to remove ambiguous situations. If marked, it is shown at the end of the noun. Further information on the types of declensions is discussed in the following section, along with examples. Grammatical case endings are not pronounced in pausa and in less formal forms of Arabic. Note that in vocalised Arabic (where vowel points are written), the case endings may be written even if they are not pronounced. Some Arabic textbooks or children's books skip case endings in vocalised Arabic, thus allowing both types of pronunciation. Nominative case. The nominative ( ) is used in several situations: For singular  nouns and broken plurals, it is marked as a "usually unwritten" ' () for the definite or ' + nunation () for the indefinite. The dual and regular masculine plural are formed by adding -an(i) and respectively (just - and - in the construct state). The regular feminine plural is formed by adding in the definite and in the indefinite (same spelling). Accusative case. The accusative ( ) has several uses: For singular nouns and broken plurals, it is marked as a usually unwritten ' () for the definite or ' + nunation () for the indefinite. For the indefinite accusative, the ' + nunation is added to an ', e.g. , which is added  to the ending of all nouns not ending with a ' followed by ' or a ". Note that this is the only case (when alif is written), which affects the unvocalised "written" Arabic (e.g. ). The dual and regular masculine plural are formed by adding and respectively (spelled identically!) ( and in the construct state, again, spelled identically). The regular feminine plural is formed by adding in the definite and in the indefinite (spelled identically). Some forms of indefinite accusative are mandatory even for spoken and pausal forms of Arabic, sometimes is changed to a simple in pausa or spoken Arabic. Diptotes never take  an alif ending in the written Arabic and are never pronounced with the ending . Genitive case. The genitive case (", ) For singular nouns and broken plurals, it is marked as a usually unwritten ' (') for the definite or ' + nunation (') for the indefinite. The dual and regular masculine plural are formed by adding ' and ' respectively (spelled identically) ( ' and ' in the construct state, again, spelled identically). The regular feminine plural is formed by adding ' in the definite and ' in the indefinite (spelled identically in Arabic). Types of declension. Fully declined nouns (triptotes). For fully declined nouns, known as "triptote" ( '), that is, having three  separate case endings, the suffixes are ', ', ' for nominative, accusative, and genitive case respectively, with the addition of a final (nunation, or ') to produce ', ', and ' when the word is indefinite. This system applies to most singular nouns in Arabic. It also applies to feminine nouns ending in ' ("") and hamzah, but for these, alif is not written in the accusative case. It also applies to many "broken plurals". When words end in ' ("") the ' is pronounced when the case ending is added; thus ("message") is pronounced ' in pausal form, but in Classical Arabic it becomes ', ', and "" when case endings are added (all usually  spelled when written without the vowel points). The final is dropped when the noun is preceded by the definite article ""). The is also dropped when the noun is used in "" (construct state), that is, when it is followed by a genitive. Thus: Nominative ( " ; literally, "raised"): Accusative ( "); literally, 'erected'): Genitive ( "; literally, 'dragged'): The final is also dropped in classical poetry at the end of a couplet, and the vowel of the ending is pronounced long. Diptotes. A few singular nouns (including many proper names and names of places), and certain types of "broken plural", are known as ( "", literally 'forbidden from inflecting ') meaning that they only have two case endings. When the noun is indefinite, the endings are ' for the nominative and ' for the genitive and accusative with no nunation. The genitive reverts to the normal ' when the diptotic noun becomes definite (preceded by ' or is in the construct state)). Diptotes never take an alif in the accusative case in written Arabic. Sound masculine plurals. In the case of sound masculine plurals ( ), mostly denoting male human beings, the suffixes are respectively "-ūna" and '. These stay the same whether ' precedes or not. The final "-a" is usually dropped in speech. In less formal  Arabic only ' is used for all cases and the final ' is dropped in pausa and in less formal Arabic. The ' is dropped when the noun is in ' (construct state). Thus: Nominative: Accusative and genitive: Note: ending "-īna" is spelled identically to "-ayni" (see above). Sound feminine plurals. In the case of sound feminine plurals ( '), the suffixes are respectively "-ātu(n)", "-āti(n)" and "-āti(n)" (identical spelling). The "n" is only there when the noun is indefinite (not preceded by '). Again the final vowel is dropped in speech and pausa, leaving only "-", making all cases pronounced identically. The final "n" is dropped when  the noun is in "" (construct state). Nominative: Accusative and genitive: Other declensional paradigms. The Dual - These nouns denote two of something. They decline very similarly to the sound masculine plurals because they are not marked for definiteness and look the same in both the accusative and genitive cases. For the nominative, the marking is "-āni" and for the accusative/genitive, "-ayni". An example is "parents," which is "wālidāni" and "wālidayni" respectively. Invariable nouns - Invariable nouns are usually those foreign names that end in "alif" or nouns that end in an additional ' or ' (when that ' or ' is not part of the  root). Also, nouns that are both and diptotic fall into this category. Additionally, there are rare invariable nouns which have other endings, like any name ending with "-ayhi," like Sībawayhi (colloquially pronounced, for example, in Egypt: . An example of a common invariable noun is ' ('), meaning 'the most eloquent [Arabic]'. Another example is ' (') 'world'. Sentence structure. A noun's case depends on the role that the noun plays in the sentence. There are multiple sentence structures in Arabic, each of which demands different case endings for the roles in the sentence. "Subject" does not always correspond to "nominative", nor does "object  always correspond to accusative". Sentences in Arabic are divided into two branches, of which are the incomplete phrases (jumla inshaiya) and the complete phrases (jumla khabariya). Jumla inshaiya is composed of the descriptive phrase and possessive phrase, while the jumla khabariya is made up of the verbal sentence (jumla fi'lya khabariya) and the nominal sentence (jumla ismiya khabariya). The incomplete phrase cannot be a sentence in itself, and is usually used in the complete phrases. Verbal sentences. In a verbal sentence ( "), there is verb–subject–object word order. This is the preferred word order of Classical Arabic. In a  verbal sentence, the subject takes nominative case and the object takes accusative case. Such a sentence ("This writer wrote the written") would be formed as follows (read from right to left): Nominal sentences. In a nominal sentence ( "), there is subject–verb–object word order. Equations (no copula verb). If the verb would be "is" (that is, the predicate merely attributes something to the subject—see Predicative (adjectival or nominal)), then there is no verb used. Both the subject and the predicate take nominative case when there is no overt verb. Such a sentence ("This writer is famous") is formed as  follows (read from right to left): Overt verb. If there is an overt verb, the subject takes nominative and the predicate takes accusative. Such a sentence ("This writer wrote the book") is formed as follows (read from right to left): Sisters of "inna". There is a class of words in Arabic called the "sisters of " ( "") that share characteristics of . Among them are: If one of the sisters of begins a clause, then the subject takes accusative case instead of nominative. Such a sentence using the particle ("Verily, this writer wrote the book") would be formed as follows (read from right  to left): Note that although there was an overt verb in the above example, a nominal sentence without an overt verb will also have its subject take accusative case because of the introduction of one of 's sisters. (The predicate of an equation is unaffected and will remain in the nominative.) Consider the following example ("Verily, this writer is famous"): With sisters of "kāna". The verb () and its sisters ( "") form a class of 13 verbs that mark the time/duration of actions, states, and events. Sentences that use these verbs are considered to be a type of nominal sentence according  to Arabic grammar, not a type of verbal sentence. Although the word order may seem to be verb–subject–object when there is no other verb in the sentence, note that it is possible to have a sentence in which the order is "subject–verb–object". Such a non-equation sentence clearly shows subject–verb–object word order. Among the sisters of kāna are: If one of the sisters of begins a clause, then the subject takes nominative case and the object takes accusative case. (Note that because of this, Arabic contrasts "[The man] is [a doctor]" in the present  tense with "[The man] was [a doctor]" in the past tense.) Such a sentence using the verb ("This writer was famous") would be formed as follows (read from right to left): In a sentence with an explicit verb, the sister of kāna marks aspect for the actual verb. A sentence like (was the.writer he.writes the.book, 'the writer was writing the book'), for instance, has both a main verb () and a sister of kāna that indicates the non-completed aspect of the main verb. Verbs. The imperfective tense of the verb also has suffixed vowels, which determine the mood of the  verb, There are six moods in the Classical Arabic, Thus: All the first three forms are spelled in unvocalised Arabic, and the final vowel is not pronounced in pausa and in informal Arabic, leaving just one pronunciation: ". Traditional Arab grammarians equated the indicative with the nominative of nouns, the subjunctive with the accusative, and the jussive with the genitive, as indicated by their names (the only pair that is not borne out in the name is the jussive-genitive pair, probably because the "" vowel is usually dropped). It is not known whether there is a genuine historical connection or whether  the resemblance is mere coincidence, caused by the fact that these are the only three short vowels available.