This paper compares transformation-based and constraint-based treatments of unbounded filler-gap dependencies, the latter specifically as articulated in terms of HPSG, and argues, contrary to the commonly made allegations of notational variance , that there is purely empirical evidence that is consistent with only the constraint-based account. Recent proposals to deal with parasitic gaps in terms of null pronominals and empty operators are unable to account for the phenomenon of symbiotic gaps, the apparent case mismatches found in parasitic gap constructions, or (in general) for the well-known across-the-board effects within coordinate structures.