8.2.1 Raising
In this way, each clause is provided with a subject, the trace, and hence the EPP can be satisfied. The ungrammaticality of (63) demonstrates that when a subject raises, it cannot actually be moved too far. Looking at what is possible and what is not possible with such movements, there is something similar about the restriction to the restriction we have noted concerning head movement. Recall that he Head Movement Constraint demands that heads do not move over the top of other heads. It appears that the restriction on subject movement is that it cannot cross over the top of another subject. A general way to express both these restrictions is to claim that a moving element cannot move over the top of a like element. This principle, known as Relativized Minimality, was introduced by Rizzi (1990) as a way of accounting for locality conditions on movement. The following diagram might help to make clear how the principle works: