Ross B. Grantham (The University of Queensland – T.C. Beirne School of Law) has posted A Normative Account of Defences to Restitutionary Liability (Cambridge Law Journal, March 2008) on SSRN. Here is the abstract:
The aim of this paper is to offer an account of how the defences that on orthodox views are regarded as central to restitutionary claims may be incorporated into the broader normative structure of restitutionary liability. The paper will seek to outline what the normative structure of restitutionary liability indicates about the general shape and focus of the defences. It will then suggest how the various defences may be understood in terms consistent with the normative structure of restitutionary liability.