أَأْمَنَ → آمَنَ
The first hamzah bears fatḥah; the second is quiescent. Replacing the second with alif gives آمَنَ, “he believed.”
In this Form IV verb, the added initial hamzah meets the root-initial hamzah. The resulting long vowel is the outcome of an operation; it does not mean that the original root lacked hamzah.
Classifying آمَنَ as an inherently weak root merely from its surface long vowel would miss the derivation.
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How آمَنَ Is Formed
Rules of Hamzated Forms: Lightening, Substitution, Elision and Short Paradigms
أَأْمَنَ → آمَنَ
The first hamzah bears fatḥah; the second is quiescent. Replacing the second with alif gives آمَنَ, “he believed.”
In this Form IV verb, the added initial hamzah meets the root-initial hamzah. The resulting long vowel is the outcome of an operation; it does not mean that the original root lacked hamzah.
Classifying آمَنَ as an inherently weak root merely from its surface long vowel would miss the derivation.