Implicit ⇒ imaginative
If implicit metaphor always carries an imaginative feature, then the presence of an implicit metaphor entails the presence of that feature.
The reverse statement, imaginative ⇒ implicit, does not follow automatically. A particular tree is a plant, but not every plant is that particular tree. In the same way, each direction of dependence among rhetorical categories needs independent support.
The source’s objections question, on one side, the possibility of an implicit metaphor without imagination, and, on the other, whether an imaginative clue is the only possible way of signaling an implicit metaphor.