Grammar term · Sarf · morphology
إِعْلَال بِالْقَلْب
i'lal bi-l-qalb
Weak-letter substitution (i'lal by qalb)
Sarf · morphologyMorphophonemic processadvanced term8,061+ in the Qur'an
In one line
Weak-letter flipping: one weak letter becomes another — the waw of قَوَلَ turns into the alif of قَالَ.
Classical definition
الإِعْلَالُ بِالقَلْبِ قَلْبُ حَرْفِ العِلَّةِ حَرْفَ عِلَّةٍ آخَرَ، كَقَلْبِ الوَاوِ أَلِفًا فِي قَالَ.
“I'lal by conversion is the turning of a weak letter into another weak letter, like the waw becoming alif in qala.”
(بتصرف من شذا العرف)
Key words in the Arabic
قَلْبflipping, conversion
حَرْف عِلَّة آخَرanother weak letter
Understand it
The headline rule: a waw or ya with a vowel, sitting after a fatha, flips to alif — so قَوَلَ became قَالَ, بَيَعَ became بَاعَ, دَعَوَ became دَعَا. Other flips follow their own triggers: waw to ya after kasra (مِيزَان from مِوْزَان), ya to waw after damma. Every 'irregular' hollow and weak-tailed verb is just this rule applied consistently.
How to spot it
Recognition test
See an alif where the root has waw or ya: qalb has applied. Recover the root from the mudari' or the masdar and the flip becomes visible.
In the Qur'an
وَقَالَ رَبُّكُمُ ٱدْعُونِىٓ أَسْتَجِبْ لَكُمْ
Ghafir 40:60 — “And your Lord says: Call upon Me — I will respond to you”
قَالَ — the root waw of قول, vowelled after a fatha, has flipped to alif: i'lal bil-qalb.
Related terms