It will be argued in this paper that there is no good reason to limit the offensive effect of equitable estoppel to its proprietary form, which is narrowly focused on property rights in land. This paper elucidates the differences between promissory and proprietary estoppel, and ask if the differences in the elements of each doctrine can explain why only proprietary estoppel enjoys offensive effect.
What’s Special About Land? the Relationship Between Promissory and Proprietary Estoppel. King’s Law Journal, Hart Publishing Vol 24, Number 1, pp. 111-118 (8).