Parasitic gap


In generative grammar, a parasitic gap is a construction in which one "gap" appears to be dependent on another "gap", that is, 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, e.g. Which explanation did you reject __1 without first really considering __2? While parasitic gaps are present in English and some related Germanic languages, e.g. Swedish, 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 following b-sentences illustrate typical parasitic gaps. The parasitic gaps are marked with a p-subscript:
The a-sentences are normal declarative sentences that contain no gaps at all. Each b-sentence, in contrast, contains two gaps, whereby the second gap is parasitic on the first. The c-sentences illustrate that if there is no "real" gap, the parasitic gap is not possible. One interesting thing about parasitic gaps like the ones here in the b-sentences is their motivation. Their appearance appears to be reliant on syntactic movement. The fact, however, that there are two gaps in each b-sentence but only one fronted wh-expression is a source of the difficulty associated with the construction. How does it come to pass that one fronted wh-expression is capable of licensing two gaps? Another interesting fact about parasitic gaps is that they usually appear inside extraction islands, hence one might expect extraction from the site of parasitic gaps to be altogether impossible. The fact that the islands are ignored is a second source of challenge associated with the phenomenon.

Some historical notes

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 knowledge of parasitic gaps was central to the development of the GPSG framework in the mid 1980s, this knowledge then being refined later in the HPSG framework of Carl Pollard and Ivan Sag. In the 90s, a debate centered around the best theoretical analysis of parasitic gaps, this debate culminating in a collection of essays edited by Peter Culicover and Paul Postal in 2001.

Some traits of parasitic gaps

The following subsections briefly explore some aspects of parasitic gaps that have been widely acknowledged in the literature on parasitism. The following areas are addressed:
  1. many parasitic gaps appear optionally;
  2. some parasitic gaps appear obligatorily;
  3. parasitic gaps appear in missing object constructions; and
  4. syntactic parallelism seems to promote the appearance of parasitic gaps.

    Optional parasitic gaps

Many parasitic gaps appear optionally. They are in non-complementary distribution with a pronoun, meaning that the speaker has the choice whether to employ the gap or not, e.g.
The a-sentence contain typical parasitic gaps, whereas the b-sentence choose to use a pronoun instead of the gap. In other words, the parasitic gap in the a-sentences is occurring optionally. Optionality like this suggests an analysis of parasitism in terms of ellipsis, since optionality is the primary trait of known ellipsis mechanisms.

Obligatory parasitic gaps

While many parasitic gaps occur optionally as just illustrated, other parasitic gaps occur obligatorily. This can be the case when the parasitic gap precedes the "real" gap, e.g.
These examples illustrate a couple of important facts about parasitic gaps. The b-sentences demonstrate that the parasitic gap can indeed precede the "real" gap, and the strong marginality of the c-sentences shows that in a sense, the real gap can also be dependent on the parasitic gap. Note that we know that the first gap in the b-sentences is parasitic on the following gap because it, i.e. the leftmost gap, appears inside what is normally an extraction island. The aspect of parasitic gaps illustrated with these examples is addressed in terms of the weak crossover phenomenon. The WCO phenomenon occurs when a fronted expression is coreferential with an intermediate expression that appears between the fronted expression and the position of its gap. In the big picture, one can simply note that parasitic gaps behave variable depending upon whether they precede or follow the "real" gap. When they precede the "real" gap, their appearance is usually obligatory.

Missing object constructions

Much work on parasitism assumes that parasitic gaps are dependent on another gap, the "real" gap in the examples above. Hence the assumption is that parasitic gaps are reliant on those mechanisms that license normal extraction gaps, e.g. wh-movement and topicalization. This assumption is challenged, however, by so-called missing-object constructions, e.g.
The a-sentences lack gaps entirely. The b-sentences contain parasitic gaps despite the fact that neither wh-movement nor topicalization has occurred. The b-sentences illustrate missing-object constructions, since the verbs appreciate, understand, and get are transitive and should hence take an object. This object is missing, as marked by the gap on the left. Whatever the analysis of parasitic gaps ends up being in the long run, it will have to accommodate the facts involving missing objects illustrated here. Movement may actually not be the key factor licensing parasitic gaps.

The role of parallelism

Examining the examples of optional parasitic gaps produced above so far, one sees that in each case, a certain parallelism is present. This parallelism is now illustrated using brackets:




In each of these examples, the square brackets mark what appear to be parallel structures, as associated with the coordinate structures of coordination. The brackets mark verb phrases, whereby the subordinator appearing between the brackets is functioning like a coordinator. This parallelism may be a significant factor that is aiding the appearance of the parasitic gaps. When this parallelism is absent, there is a significant drop in acceptability of the parasitic gap:


These instances of parasitic gaps are all marginal to varying degrees. The marginality is probably due to the lack of syntactic parallelism indicated by the brackets, the gaps no longer appearing on the same side of the brackets. In any case, there is a noticeable drop in acceptability when the parallelism in the examples further above is removed. What exactly explains this drop in acceptability is not entirely clear, although it may have to do with ease of processing. Parallel structures are easier for humans to process, and hence parasitic gaps are reliant on a low processing load.

Theoretical controversy

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 first is to assume that parasitic gaps are extraction gaps ; 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. The alternative approach rejects the analysis that takes parasitic gaps to be extraction gaps. One assumes instead that parasitic gaps actually contain a covert element, this element having the status of definite proform.. 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.
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. 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. The 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.