In سُؤَالٌ, hamzah itself bears fatḥah, yet the eased substitute is wāw. Rule 4 bases the substitute on the preceding ḍammah, not the hamzah's own fatḥah.
As the rule states more generally, preceding kasrah calls for yāʾ instead.
Consequently, identifying the vowel of hamzah alone is not enough. A correct analysis must also identify the vowel immediately before it.
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Which Vowel Determines سُؤَالٌ?
Rules of Hamzated Forms: Lightening, Substitution, Elision and Short Paradigms
In سُؤَالٌ, hamzah itself bears fatḥah, yet the eased substitute is wāw. Rule 4 bases the substitute on the preceding ḍammah, not the hamzah's own fatḥah.
As the rule states more generally, preceding kasrah calls for yāʾ instead.
Consequently, identifying the vowel of hamzah alone is not enough. A correct analysis must also identify the vowel immediately before it.