There are also several theoretical approaches to sluicing that do not involve the movement of the wh-phrase out of the embedded clause. These approaches include PF deletion and LF copying. PF deletion as proposed by
Howard Lasnik states that the TP within the embedded clause is null and has syntactic structure within it that is elided following a wh-movement operation. The other approach, LF copying, is a process proposed by
Anne Lobeck in which the original structure of a sluicing phrase is one in which the wh-word originates in the SpecCP position of the embedded clause and a null phrase marker (marked
e) occupies the position of the tense phrase of the embedded clause. This is the extent of the syntactic derivation. After this structure is derived, it is
sent off for semantic interpretation, to logical form, in which the implied material in the tense phrase is then present for our full understanding of the sentence. The evidence for this approach is that it is able to account for islands in sluicing as is discussed below. == Islands in sluicing ==