[1] Coreference (or coindexation) that is normal and natural when a pronoun follows its antecedent becomes impossible, or at best just marginally possible, when "crossover" is deemed to have occurred, e.g. ?Who1 do his1 friends admire __1?
The gaps in the b-sentences mark the canonical position of the wh-expression (before movement): The acceptability contrast here is curious upon first analysis.
The relevant difference is that in the b-sentences, the wh-expression appears to have been moved across the pronoun on its way to the front of the sentence, whereas there is no such crossover in the a-sentences.
[3] Postal suggests the idea of "scope islands" may play a role in the observance of crossover phenomena when operators are not the moving element.
The crucial element that divides these essentially minimal pairs is the status of the pronoun, which is in the bracketed constituents below:a. Sidney1, I am sure [his1 job] is important to ___1.
*Ted1, who1 I am sure that [your dismissal of him1] has driven ___1 mad, … - "scope island" restricts the scope to phrase internal, intentional coreferential reading unlikelyThe observation to be made is that crossover effects also seem to arise when the pronoun being crossed over is embedded in a noun phrase and the item doing the movement is not an operator.
In the underlying structure (before movement) the antecedent (the pronoun) c-commands an R-expression (the wh-expression) which violates Condition C of binding theory and therefore could explain why a coreferential reading is unavailable in cases of strong crossover.
Typical cases of weak crossover occur when the expression that has been "crossed over" is a possessor inside a noun phrase, e.g.
However, weak crossover effects are absent when the pronoun is contained within an adjunct phrase, for example: Based on this observation, Stowell proposes the following analysis of weak crossover: “In a configuration where a quantifier Q locally binds a pronoun P and a trace T, P may not be contained in an argument phrase XP that c-commands T.”[5] There are certain syntactic phenomena in which we would expect weak crossover effects to arise, however we find that they are absent and a coreferential reading is possible, e.g.
Simple linear order plays a role, but the other key factor might be c-command as associated (primarily) with government and binding, or it might be o-command as associated with head-driven phrase structure grammar.
[6] Therein, crossover phenomena are said to occur when a previous binding/co-indexing relationship between (typically) an operator and a pronoun becomes unavailable after the fronting of a constituent.
Adesola (2006) describes a process by which Yoruba (and its related languages) avoids crossover effects in wh-movement via null operator raising.