The chief function of the ECP is to place constraints on the movement of categories by the rule of move α; it effectively allows a tree structure to "remember" what has happened at earlier stages of a derivation, and it can be seen as GB's version of the older derivational constraints.
ECP is designed to impose limits on category shifts through the move α rule. This enables a tree structure to remember past derivation stages and operates similarly to GB’s previous derivational constraints.