Can text structure be incompatible with rhetorical structure?

Scott and Souza have posed the problem of how a rhetorical structure in which proposi tions are linked by rhetorical relations but not yet arranged in a linear order can be realized by a text structure in which propositions are ordered and linked up by appropriate discourse connectives Almost all work on this problem assumes implicitly or explicitly that this map ping is governed by a constraint on compatibil ity of structure We show how this constraint can be stated precisely and present some coun terexamples which seem acceptable even though they violate compatibility The examples are based on a phenomenon we call extraposition in which complex embedded constituents of a rhetorical structure are extracted and realized separately