In generative grammar, a parasitic gap is a construction in which one gap appears to be dependent on another gap. Thus, the one gap can appear only by virtue of the appearance of the other gap, hence the former is said to be "parasitic" on the latter. For example, in the example sentence in (1) the first gap is represented by an underscore ( __ ), and appears as a result of movement of the constituent which explanation to the beginning of the sentence. The second gap is represented by an underscore with a subscript p ( __p); this is the "parasitic gap".
While parasitic gaps are present in English and some related Germanic languages, e.g. Swedish (see Engdahl 1983), their appearance is much more restricted in other, closely related languages, e.g. German and the Romance languages. Japanese linguistic scholar Fumikazu Niinuma has attempted to differentiate between parasitic gaps and coordination in his research, as he believes the two are often confused. An aspect of parasitic gaps that makes them particularly mysterious is the fact they usually appear inside islands to extraction. Although the study of parasitic gaps began in the late 1970s, no consensus has yet been reached about the best analysis.
The phenomenon The example sentences in (2) are normal declarative sentences that contain no gap at all. The sentences in (3), in contrast, contain two gaps, whereby the second gap is parasitic on the first; the parasitic gap is marked with a p-subscript. The sentences in (4) show that if there is no real gap (that corresponds to the bold-faced constituent), then the parasitic gap is not possible.
The appearance of parasitic gaps in (3) appears to be reliant on syntactic movement (e.g. wh-movement or topicalization), and presents two challenges:
The fact that there are two gaps but only one fronted wh-expression is a source of difficulty for the analysis of parasitic gap constructions. Why can one fronted wh-expression license two gaps? The fact that parasitic gaps usually appear inside extraction islands leads one to expect extraction from the site of the parasitic gap to be altogether impossible. Why do parasitic gaps ignore islands?.
History
Discovery The phenomenon of parasitic gaps appears to have been discovered by John Robert Ross in the 1960s, but remained undiscussed until papers by Knut Tarald Taraldsen and Elisabet Engdahl explored the properties of the phenomenon in detail. The analysis of parasitic gaps was central to the development of the GPSG framework (Generalized Phrase Structure Grammar) in the mid-1980s, and this analysis was later refined in the HPSG framework (Head-driven Phrase Structure Grammar) of Carl Pollard and Ivan Sag. In the 1990s, a debate centered around the best theoretical analysis of parasitic gaps, namely extraction versus percolation. This debate culminated in a collection of essays edited by Peter Culicover and Paul Postal in 2001.
Controversy
Extraction gap versus proform The theoretical analysis of parasitic gaps is not a settled matter by any means, since accounts of the phenomenon vary drastically. In very broad terms, there are two lines of analysis that one can pursue:
The extraction analysis assumes that parasitic gaps are extraction gaps, and that parasitic gaps arise by way of the same basic mechanism that licenses "normal" extraction gaps. This sort of approach must augment the analysis of extraction gaps in some way in order to accommodate parasitic gaps under the same theoretical umbrella. Extraction analyses have the advantage that they immediately accommodate the simple observation that most parasitic gaps appear to be dependent on the occurrence of wh-movement or topicalization. Extraction analyses are challenged, however, by missing-object constructions, as noted above. The proform analysis assumes that parasitic gaps actually contain a covert element, this element having the status of definite proform. Proform analyses have the advantage that they immediately accommodate the simple observation that many parasitic gaps occur optionally; the covert proform has the option to be overt. Proform analyses are challenged, however, by the fact that most parasitic gaps occur in the immediate environment of wh-movement or topicalization, since they do not provide a clear basis for explaining this correlation. Some analyses mix and match these two basic lines of analysis, although in general, both are well represented in the literature on parasitism and most accounts can be placed in the one or the other camp.
Licensing of real gap The controversy regarding the licensing of parasitic gaps has also been widely debated as the phenomenon has continued to be researched. It is generally agreed upon that a real gap licenses a parasitic gap however, the required properties of this real gap have been widely debated. In 1994, Postal wrote a paper examining how the leftward extraction of clauses may be a general licensor for parasitic gaps while examining two theoretical approaches:
P-Gap Licensing Restriction (PLR) suggests that the gaps that license parasitic gaps must be restricted in some way. PG=NP suggests that the licensors of parasitic gaps must be NPs/DPs. On the basis of evidence from topicalization and object raising, Postal's 1994 paper concludes that true parasitic gaps are not licensed by rightward DP movement, but rather by leftward extraction of a clause. Overfelt 2016 argues against Postal's claim that rightward DP movement cannot license true parasitic gaps, and concludes that the licensors of true parasitic gaps are adjunction structures.
Some traits of parasitic gaps Some of the central research issues that arise in the investigation of parasitic gaps include:
optionality: many parasitic gaps are optional obligatoriness: some parasitic gaps are obligatory missing object: the appearance of parasitic gaps in missing object constructions (also known as tough-movement) parallelism: syntactic parallelism seems to promote the appearance of parasitic gaps
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