A proper name such as «Zayd» normally points to an identified individual, while a descriptive term such as «the departing one» or «the generous one» adds a feature or characterization. When both appear as definite expressions, the hearer must determine which is the topic and which is the assertion.
Examples:
«زَيْدٌ الْمُنْطَلِقُ» — A known description of departing is predicated of Zayd.
«الْمُنْطَلِقُ زَيْدٌ» — The previously known departing person is identified as Zayd.
A definite expression does not always function merely as an isolated external individual; it may also organize the attribute, category or relation relevant to the assertion. Syntax by itself is therefore insufficient.