This paper considers the utility of the concept of conscience or unconscionable conduct as a contemporary rationale for intervention in two principles applied where a person seeks to renege on an informal agreement relating to land: the principle in Rochefoucauld v Boustead; and transfers ‘subject to’ rights in favour of a claimant. By analysing the concept in light of our current understanding of the nature of judicial discretion and the use of general principles, it responds to arguments that unconscionability is too general a concept on which to base intervention. In doing so, it considers the nature of the discretion that is actually in issue when the court intervenes through conscience in these principles. However, the paper questions the use of constructive trusts as a response to unconscionability. It argues that there is a need, in limited circumstances, to separate the finding of unconscionability from the imposition of a constructive trust. In these limited circumstances, once unconscionability is found, the courts should have a discretion as to the remedy, modelled on that developed in the context of proprietary estoppel. The message underlying this paper is that many of the concerns expressed about unconscionability that have led to suggestions of alternative rationales for intervention can in fact be addressed whilst retaining an unconscionability analysis. Unconscionability remains a preferable rationale for intervention as it provides a common thread that links apparently separate principles and can assist our understanding of their scope.