Parasitic gap

In the study of syntax, 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. 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.