Modifications: Zihafs and Ellals (الزحافات والعلل)

In Arabic Prosody, the standard feet (Taf'ilas) are ideal templates. Real poetry often modifies these templates for musical variation or necessity. These modifications are strictly categorized into Zihafs and Ellals.

1. Zihaf (الزحاف)

Definition: A change that affects the Sabab (Cord) letters in the foot. - Scope: Can occur in the Hashw (interior feet), Arudh (end of 1st hemistich), or Dharb (end of 2nd hemistich). - Consistency: Generally not binding (Ghayr Lazim). If a poet uses a Zihaf in one verse, they are not required to use it in the next (with some exceptions).

Single Zihafs (الزحاف المفرد)

Changes involving only one letter.

Name (Arabic)	Name (English)	Definition	Effect	Example
الإِضْمَار	Idmar	Quieting the 2nd letter.	`11...` $\rightarrow$ `10...`	`Mutafa'ilun` $\rightarrow$ `Mutfa'ilun`
الْخَبْن	Khaban	Deletion of the 2nd letter.	`10...` $\rightarrow$ `1...`	`Mustaf'ilun` $\rightarrow$ `Mutaf'ilun`
الْوَقْص	Waqas	Deletion of the 2nd letter (if moving).	`11...` $\rightarrow$ `1...`	`Mutafa'ilun` $\rightarrow$ `Mufa'ilun`
الطَّي	Tay	Deletion of the 4th letter.	`...10...` $\rightarrow$ `...1...`	`Mustaf'ilun` $\rightarrow$ `Musta'ilun`
الْعَصْب	Asab	Quieting the 5th letter.	`...11...` $\rightarrow$ `...10...`	`Mufa'alatun` $\rightarrow$ `Mufa'altun`
الْقَبْض	Qabadh	Deletion of the 5th letter.	`...10...` $\rightarrow$ `...1...`	`Fa'ulun` $\rightarrow$ `Fa'ulu`
الْعَقْل	Akal	Deletion of the 5th letter (if moving).	`...11...` $\rightarrow$ `...1...`	`Mufa'alatun` $\rightarrow$ `Mufa'atun`
الْكَف	Kaff	Deletion of the 7th letter.	`...10` $\rightarrow$ `...1`	`Fa'ilatun` $\rightarrow$ `Fa'ilatu`

Double Zihafs (الزحاف المزدوج)

Changes involving two letters in the same foot.

Name (Arabic)	Name (English)	Combination	Example
الْخَبْل	Khabal	Khaban + Tay	`Mustaf'ilun` $\rightarrow$ `Mu'ta'ilun`
الْخَزْل	Khazal	Idmar + Tay	`Mutafa'ilun` $\rightarrow$ `Mutfa'il`
الشَّكْل	Shakal	Khaban + Kaff	`Fa'ilatun` $\rightarrow$ `Fa'ilatu`
النَّقْص	Nakas	Asab + Kaff	`Mufa'alatun` $\rightarrow$ `Mufa'altu`

2. Ellah (العلة)

Definition: A change that affects the Watad (Peg) or the ending of the foot. - Scope: Only occurs in the Arudh and Dharb (the ends of hemistiches). - Consistency: Binding (Lazim). Once a poet uses an Ellah in the first verse, they must maintain it throughout the entire poem.

Ellal of Increase (علل الزيادة)

Adding letters to the foot. Occurs mostly in Majzoo meters.

Name (Arabic)	Name (English)	Definition	Example
التَّرْفِيل	Tarfeel	Adding a Sabab Khafif (`10`) to the end.	`Fa'ilun` $\rightarrow$ `Fa'ilun-tun` (`Fa'ilatun`)
التَّذْيِيل	Tatheel	Adding a Sakin letter to a Watad Majmu'.	`Fa'ilun` $\rightarrow$ `Fa'ilan`
التَّسْبِيغ	Tasbeegh	Adding a Sakin letter to a Sabab Khafif.	`Fa'ilatun` $\rightarrow$ `Fa'ilatan`

Ellal of Decrease (علل النقص)

Removing letters from the foot.

Name (Arabic)	Name (English)	Definition	Example
الْحَذْف	Hadhf	Dropping the final Sabab Khafif.	`Fa'ulun` $\rightarrow$ `Fa'u`
الْقَطْف	Qataf	Dropping Sabab + Asab (Quieting 5th).	`Mufa'alatun` $\rightarrow$ `Fa'ulun`
الْقَطْع	Qataa	Cutting the tail of Watad Majmu' & quieting predecessor.	`Fa'ilun` $\rightarrow$ `Fa'il`
الْبَتْر	Batr	Hadhf + Qataa (Extremity).	`Fa'ulun` $\rightarrow$ `Fa`
الْقَصْر	Qasar	Dropping the Sakin of Sabab Khafif & quieting the mover.	`Fa'ilatun` $\rightarrow$ `Fa'ilat`
الْحَذَذ	Hathath	Dropping a full Watad Majmu'.	`Mutafa'ilun` $\rightarrow$ `Mutfa`
الصَّلْم	Salam	Dropping a full Watad Mafruq.	`Maf'ulatu` $\rightarrow$ `Maf'u`
الْكَشْف	Kashf/Kasf	Dropping the last letter of a Watad Mafruq.	`Maf'ulatu` $\rightarrow$ `Maf'ula`
الْوَقْف	Waqf	Quieting the last letter of a Watad Mafruq.	`Maf'ulatu` $\rightarrow$ `Maf'ulat`

3. How PyArud Validates Modifications

PyArud does not just "guess" modifications. Each Tafeela class in the code has a list of allowed_zehafs.

For example, Mustafelon allows Khaban and Tay. When analyzing a verse, PyArud generates all mathematically valid permutations of Mustafelon (e.g., 1010110, 110110, 101010) and tries to match them against your text.

If a modification is found, the analysis result will explicitly state the status and the expected pattern versus the actual segment, allowing you to trace exactly which rule was applied.