HPSG accounts of filler-gap dependencies hold considerable
potential for explaining the cross-linguistic variation in
unbounded dependency constructions (UDCs), specifically filler-gap
dependencies. This potential comes from the SLASH
specifications that are posited in all nodes along the extraction
path (the path between filler and gap). However, as Hukari and
Levine (1994, 1995, 1996) have observed, the HPSG analysis
presented by Pollard and Sag (1994) fails to embody the
generalizations required in order to explain key universal
properties of UDCs, in particular the ˋregistration' of such
dependencies in cases of subject- and adverb-extraction. This
demonstration led Bouma et al. (2001) to propose a revised UDC
analysis that avoids these difficulties by ˋthreading' the SLASH
specfications through all heads within an extraction
domain. However, Levine (2002) points out that this analysis
encounters a new difficulty concerning the interaction of
extraction and coordination. This paper revisits these issues,
arguing that a small modification of the BMS analysis provides a
solution to the important problem observed by Levine.