In linguistics, pied-piping is a phenomenon of syntax whereby a given focused expression brings along an encompassing phrase with it when it is moved.
In syntactic pied-piping, a focused expression (such as an interrogative word) pulls its host phrase with it when it moves to its new position in the sentence.
[5] In English, pied-piping occurs when a wh-expression drags its containing phrase with it to the front of the clause.
In the following examples, the focused expression is indicated in bold, and the fronted word/phrase in the (b) and (c) sentences is underlined, with the gap marking its canonical position.
Pied-piping also occurs in embedded wh-clauses: In (4), the possessive interrogative whose is contained within a determiner phrase (DP) that also includes paper.
In cases where pied-piping and preposition stranding are interchangeable, both types of constructions are generally considered acceptable by native English speakers.
[12] Preposition pied-piping is favoured in formal registers of English, such as academic writing and printed text.
[15] This occurs with some antecedent nouns (e.g., way, extent, point, sense, degree, time, moment) and some prepositions (e.g., beyond, during, underneath).
If one views just part of a topicalized or extraposed phrase as focused, then pied-piping can be construed as occurring with these other types of discontinuities.
Assuming that just the bolded words in these examples bear contrastive focus, the rest of the topicalized or extraposed phrase is pied-piped in each (b) sentence of (14) and (15).
When the leftmost NP moves, pied-piping is necessary in order to ensure that the Left Branch Condition is not violated.
[24] The fact that pied-piping varies so much across languages is a major challenge facing theories of syntax.
To ensure grammaticality, the larger DP must move whereby the interrogative whose pied-pipes the NP complement paper, seen in (4b).
As theories of syntax evolved, linguists have investigated the phenomenon of pied-piping in English and other languages using different syntactic models.
The following examples from Russian, Latin, and German illustrate variation in pied-piping across languages.
In some cases, relative pronouns in German have the option to pied-pipe a governing zu-infinitive when they are fronted.