This paper presents a novel analysis of Sluicing, an ellipsis construction first described by Ross (1969) and illustrated by the bracketed portion ofI want to do something, but I'm just not sure [what _]. Starting from the assumption that a sluice consists of a displaced Wh-constituent and an empty IP, we show how simple and general LF operations fill out the empty IP and thereby provide it with an interpretable Logical Form. The LF operations we appeal to rely on the (...) influential theory of indefinites developed by Irene Heim and Hans Kamp, and are in harmony with certain aspects of Chomsky's Minimalist Program for linguistic theory. The analysis accounts directly for the familiar properties of Sluicing, as well as some facts which have not previously been observed. (shrink)