Unlike other constructions, coordinations are headless, consisting of two or more strings in coordinate function, often phrases of the same category and typically linked by means of a coordinator in marker function (mainly ‘and’, ‘or’, and ‘but’). The marker is a dependent in an expanded coordinate. Those without a marker are bare coordinates.

A coordination is permitted roughly wherever all of its coordinates, unlimited in number, would be permitted. Coordinates are required to be syntactically similar in potential function.

The order of coordinates is not always free. When the order of a pair of coordinates may be switched, they are symmetric. Otherwise, they’re asymmetric. An expanded coordinate can never be preposed. Sometimes semantic considerations require a particular order, and some coordinates are fixed phrases. The interpretation of a coordination may be joint or distributive.When a coordinate itself is a coordination, the coordinations are said to be layered. Finally, we note a number of Non-basic cases: expansion of coordinates by adjuncts, gapped coordination, coordination of non-constituents, delayed right constituent coordination, and end-attached coordinates.

This chapter applies the double-Headed analysis to the different types of relative clauses attested cross-linguistically (Externally Headed Post-nominal, Externally Headed Pre-nominal, Internally Headed, Double-Headed, Headless (or ‘Free’), Correlative, and Adjoined).