Merge is assumed to come free in minimalist program. The logic for this assumption is that we could not even utter a sentence because it’s the cheapest way. With Merge as an indispensible operation in grammar, this paper explores the nature of a feature that serves as the trigger of Merge. In recent terminology, the feature in question is called an edge feature EF. Based on the observation that movement always targets a functional head, this paper tries to show that non-functional lexical items really have a limitation in the number of Merge, that is to say, they can merge just once and for all.