sentences:  It is only with second-merge that order is derived out of a set {a {a, b}} which yields the recursive properties of syntax--e.g., a 'House-boat' {house {house, boat}} now reads unambiguously only as a 'kind of boat'.It is this property of recursion that allows for projection and labeling of a phrase to take place ; in this case, that the Noun 'boat' is the head of the compound, and 'house' acting as a kind of specifier/modifier.External-merge (first-merge) establishes substantive 'base structure' inherent to the VP, yielding theta/argument structure, and may go beyond the lexical-category VP to involve the functional-category light verb vP.