Sluicing

Sluicing also means extracting metals or gems in placer mining operations using a sluice box

In syntax, sluicing designates a grammatical structure in which an interrogative clause is represented only by a wh- phrase. Examples of sluicing in English include:

(1) :Phoebe wants to eat something, but she doesn't know what e.
(2) :Jon doesn't like the lentils, but he doesn't know why e.

Although sluicing is most commonly found embedded under predicates such as know or remember, matrix sluicing is also possible, as a reply to an independent utterance, e.g.,

(3) - Somebody is coming for dinner tonight.
- Who e?

Sluicing was one of the many structures identified by John Robert Ross in his 1967 dissertation, Constraints on Variables in Syntax. Sluicing raises a potential problem for syntax, as the elided content seems to form a non-constituent. Ross's solution was to analyse sluicing as involving regular wh- fronting followed by ellipsis of the sister constituent of the wh- phrase. This analysis has been expanded in greater detail by dr. Jason Merchant in his book "The syntax of silence: Sluicing, islands, and the theory of ellipsis" (2001 Oxford), which is the most comprehensive treatise on sluicing and ellipsis.