Since morphological interpretation affects in such a way the interpretive possibilities of PIs, it seems plausible to view the overtness constraint on licensers as another, perhaps indirect, consequence of morphological interpretation: some PIs need a spelled-out licenser because of their morphological makeup.
On the one hand, this must be a representation that only includes material on its way to be phonologically interpreted; if it also contained null elements, the necessity of overt licensers and the role of overtness in general would lose their explanation.
One thing that is clear is that there cannot be any question of a single affix shared by all PIs in the relevant class (or by their licensers, for that matter).
As regards their featural content, all licensers share at least one property: that of being operators, as opposed to arguments or descriptive predicates.
Just as [operator] can have many values, I take [dependent] to be a feature whose values range over the possible licensers.
The first goal of this study has been descriptive in nature: I have presented evidence that the unacceptability of some PIs inside the scope of their licensers is not a natural byproduct of semantic requirements plus the need for c-command but points to a distinct factor.
Polarity items must, by definition, lie inside the scope of their licenser; items like any N, in addition, appear to require a c-commanding and overt licenser.
Apparently, the additional requirement in these cases is that the licenser be overt.
To sum up, there is evidence that some PIs require their licenser to be overt.