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What is Cluster Reduction in Arabic?

This tutorial deals with a topic in Arabic phonology that has major repercussions in Arabic morphology. This topic is known as Cluster Reduction, and it is a set of rules designed to alleviate the difficulty in pronunciation caused by successive stops in the same syllable.  In other words, pronouncing two successive letters, both of which are ساكن, is difficult; Cluster Reduction implements rules to alter those two letters in order to create proper syllables.

Cluster reduction has implications when reading texts without vowels. Even with vowels, some texts do not implement the cluster reduction rules and the reader is left to apply them himself. Moreover, these rules play an integral role in the morphology of weak verbs.


Classical Arabic supports the following types of syllables, where the symbol C represents a consonant, the symbol V represents a vowel, and VV represents a long vowel.






















The first three types of syllables in the inventory are the primary syllables of the language. The following three are quite rare because they result in two ساكن letters occurring in succession – this phenomenon is formally known as اجتماع الساكنين. In particular, syllable types 4 and 5 are only tolerated during stops (وقف) and there must be a set of rules implemented to transform these into proper syllables of type 1, 2, or 3 if they occur anywhere else. The rest of this tutorial deals with these rules. Syllable type 6, albeit rare, is tolerated wherever it occurs. This is because it has a long vowel followed by a geminated letter which eases the pronunciation.



اجتماع الساكنين

a succession of two letters, both of which have a سكون

In summary, therefore, syllable types 4 and 5 occur in the language. The reasons for their occurrences are numerous, including verb morphology. When their occurrence is not due to وقف, rules must be applied to alter the letters and vowels in order to form proper syllables.

Cluster Reduction

Bi-consonantal Clusters




if two non-vowelled consonants occur in succession, the first is given a كسرة.

In the vast majority of cases, two non-vowelled consonants appear in succession only across word boundaries. In other words, the last letter of a word will be ساكن and the first letter of the following word will also be ساكن. This restriction is because the internal structure of Arabic patterns are typically already secure from bi-consonantal clusters thanks to coinage.

When bi-consonantal clusters occur across word boundaries, the last letter of the first word is non-vowelled. This occurs with certain verbs (such as قُلْ), certain particles (such as مِنْ), and certain non-declinable nouns (such as مَنْ). Moreover, it may occur if the last letter of the first word has nunation, since nunation is nothing more than a نون ساكنة.

In addition, the first letter of the second word is also non-vowelled. This occurs with many verbs (such as اسْتقبل) as well as some rare nouns (such as اسْم and ابْن). But the most common occurrence is when the second word is prefixed with the definite article, Al.

The rule for bi-consonantal clusters is that the first non-vowelled letter will be given a كسرة. However, the following exceptions apply.

·         the word مِن will use a فتحة

·         plural masculine pronouns will use a ضمة

Consider the examples in the table below.

Resolved Case

Unresolved Case

قُلِ الْعفو

قُلْ الْعفو

بلِ دّارك

بلْ دّارك

مَنِ اتّقى

مَنْ اتّقى

غلامِ نِاسْمه

غلامٍ اسْمه

مِنَ الشيطان

مِنْ الشيطان

همُ الفائزون

همْ الْفائزون

أنتمُ الأْعلون

أنتمْ الأْعلون

عليكمُ الْيوم

عليكمْ الْيوم

Vowel-Consonant Clusters




if a non-vowelled consonant follows a long vowel, the long vowel is dropped.

The phenomenon of a long vowel followed by a non-vowelled consonant is not restricted to word boundaries; it may be witnessed within a single word as well. When a vowel-consonant cluster occurs, the long vowel is simply dropped to alleviate the difficulty in pronunciation. The table below gives some examples.


Resolved Case

Unresolved Case










if the cluster occurs across a word boundary, the long vowel drops only in pronunciation

ادعُـ[ـوا] الرّحمان

ادعُوْا الرّحمان

Diphthong-Consonant Clusters




if a non-vowelled consonant follows a diphthong, the diphthong is given the short vowel appropriate to it.

Just as with vowel-consonant clusters, diphthong-consonant clusters may also occur within a single word as well as across word boundaries. However, in the vast majority of cases, they occur in verbs and are rarely realized in nouns and particles.

To alleviate the pronunciation difficulty caused by diphthong-consonant clusters, the diphthong is given a suitable vowel. The vowel suitable to a واو is a ضمة, and the vowel suitable to a ياء is a كسرة.

Consider the table of examples below.

Resolved Case

Unresolved Case



رأَوُا الْعذاب

رأَوْا الْعذاب


1.       Identify the instances in the following sentences where cluster reduction should be applied

2.       Identify the type of cluster

3.       Apply the appropriate rule by pronunciation

1.       كادَتْ الجُيوشُ تَشْتَبِكُ مُجازِفةً مُقْتَحِمةً بِأَسْلِحَتِهِمْ الغَفِيْرة وفُرْسانِهِمْ الضّلِيْعة.

2.       مِنْ التُّجّارِ مَنْ اسْتَرَقَ وقالَ خُذْ المَبيعَ وسَلِّمْ البَقِيّة.

3.       قَالُوْا ابْنُوْا الصَّوْمَعةَ فَآوُوْا إليها تَعْصِمْكُمْ مِنْ سَحائِبَ حامِلةٍ الرّعْدَ والبَرْق.

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