Rule 5 records the exceptional dropping of initial hamzah in the second-person imperative كُلْ of أَكَلَ — يَأْكُلُ.
Word / formMeaning / explanation
أَكَلَhe ate.
يَأْكُلُhe eats.
كُلْeat! (masculine singular).
The root remains أ ك ل despite the absence of written hamzah in the imperative. This special form is not a license to discard hamzah from every hamzated-initial verb.