In this investigation I consider primarily coordinate structures in English, German and Dutch for determining what coordinate symmetries the semantic interface requires in them, and what these symmetry requirements suggest about the design of a generative grammar. Of particular interest is the fact that they, like many binding relations, extend across phase boundaries and thus challenge the Phase Impenetrability Condition (PIC), even without the assumption that all conjuncts are phases. I argue that if we assume that the interfaces determine conditions on the derivation, then it follows that the semantic interface must also be present at Selection so that all the semantic features required at Spell-Out are part of the numeration. The need for invasive interfaces of this sort is created by the limitations of Narrow Syntax and Selection, in particular that operations do not extend across phase boundaries and that semantic symmetry requirements are not checked in Narrow Syntax. To overcome this design limitation, I propose that many semantic symmetries are established at Selection with features chosen by an invasive semantic interface (Logical Form, LF), and that LF is also active in Narrow Syntax with feature valuation. In this way an invasive LF-interface prevents crashes at Spell-Out due to unacceptable semantic asymmetry in coordinate structures.
