This article explains the rule that leases have a certain term from the outset by placing the lease within the wider context of the system of estates in land. There are no perpetual estates in land. However, some uncertain terms risk creating genuinely perpetual estates, conflicting with the nemo dat principle. All leases for uncertain terms cause considerable difficulties if a superior estate comes to an end. The article shows that the common law addressed this difficulty, not entirely consistently, before 1925, but there are still real difficulties in the operation of escheat were uncertain terms to be permitted.
