In the multi-step movement approach, the question to model for each potential attachment site of an extraposable clause is whether the clause should move up to its grandparent (a "yes" answer) or remain attached to its current parent (a "no" answer).
the two approaches differ in their view of the movement operation: one approach models multi-step movement through intermediate nodes to the ultimate target node, while the other approach models one-step movement to the target node.