Superiority condition

Definition
Superiority condition is a condition on the application of transformations, which states that, if a transformation can in principle be applied to two constituents in the structure, it has to be applied to the one that is superior. The formal definition (from Chomsky (1973)) is as follows:

No rule can involve X,Y in the structure ...X...[...Z...-WYV...]... where the rule applies ambiguously to Z and Y and Z is superior to Y

Example
Given that wh-movement can apply only once in deriving the s-structure of a sentence, the superiority condition predicts that in structure (i) what cannot be moved: who is superior to what. The contrast in (ii) shows this prediction to be correct.

(i)		S' / \ 	     COMP S                  / \ NP  VP                |   / \ who V  NP 	          |   | saw what

(ii) a	 (I wonder) who saw what b	*(I wonder) what who saw

Links

 * Utrecht Lexicon of Linguistics