The Complainants approved a modification to a lease that allowed the Defendant to sublease the premises and left the lessee personally liable. Defendant ceased paying rent and Complainants sued to determine whether the instrument was a sublease or assignment.

A sublease grants the sublessee an interest in the lease premises with a reversionary interest remaining with the lessee. An assignment conveys the whole term, leaving no interest or reversionary interest in the lessee.
The Common law rule is if the instrument purports to transfer the lessee’s estate for the entire remainder of his term, it is an assignment, regardless of its form or the parties’ intentions. This current agreement, despite its terms, does not leave the lessee with a right to re-enter or a reversionary interest, thus it is an assignment.

Minority rule--landlord has no implied obligation to deliver actual possession. The tenant has the legal right to possession; obtaining actual possession is up to the tenant

Hannan v. Dusch

transfer of the party's entire interest under the lease. If the tenant retains any interest, it is a sublease. 

An assignment of a leasehold places the assignee in privity of estate with the landlord, meaning that the assignee and landlord are liable to each other for performance of the lease obligations that "run" with the leasehold estate