1. Under the common law, a tenant owes a covenant to maintain the premises and return it to the landlord in the same condition as it was provided. Failure to do so is called "waste," and may be "affirmative" (willful destruction), "permissive" (negligent or accidental), "amiliorative" (improvement), or "equitable" (the result of a life estate tenant who damages
the property of the remainderperson. In all cases other than amiliorative, the tenant is liable for the diminished value of the estate/property caused by the tenants acts or omissions.
The landlord owes a corresponding covenant to provide and maintain the tenant's right to the quiet enjoyment
of the tenancy. Any act or omission by the landlord, or through the landlord by an agent, is a breach of covenant, and the landlord is liable for the diminished value of the tenancy.
Each of these covenants "runs with the land" and is independent of the contractual lease.
2. A landlord can only grant to the tenant those rights in land that the landlord holds. If the landlord is a joint tenant with another person, then while the landlord can grant possession to the tenant, that possession is not exclusive, because the other joint tenant has the joint right to possess the property with the tenant. Similarly, if the landlord has mortgaged the property to a lender, then a foreclosure by the lender cuts off the tenant's lease and the tenant loses all right to occupy the property. Finally, if the "landlord" has no title to the property, then the grant of possession in a lease is a fraud, because nothing is granted and the tenant has no possessory interest in the property.
Thus, the tenant must ensure that the landlord has the right to convey exclusive possession
to the tenant, and that any loan is current -- else the tenant may find that the lease is nothing but a piece of useless paper.
3. At common law, the landlord had the right to forcibly enter the property and remove the tenant. Alternatively, the landlord could sue the tenant for ejection, prove that the tenant had breached the lease and then obtain a writ of possession to have the sheriff remove the tenant. Modernly, a landlord has the remedy of a summary process, sometimes referred to as unlawful detainer, which permits the landlord to sue for possession and obtain the writ in a relatively short period of time, as compared to what was required in an ejection suit. Throughout the USA, forcible removal of a residential tenant by a landlord is prohibited, and can subject a landlord to both civil and criminal liability.
4. A tenant is entitled to sue a landlord for a material breach of any lease covenant, and obtain damages for that breach, without surrendering the tenancy. If the breach is based upon the covenant of quiet enjoyment, the tenant can declare a constructive eviction
, vacate the premises, and sue the landlord for damages caused by the breach. In most U.S. jurisdictions, there is also an implied warranty
of habitability associated with a residential tenancy, which permits an alternative lawsuit for the landlord's failure to maintain the premises in habitable condition. This warranty is the typical action against what is commonly referred to as a "slumlord," who permits a property to decay into conditions that are considered substandard under public policy/zoning/building and safety ordinances. However, the warranty did not exist at common law, and it still does not exist with commercial leases
-- only "dwelling units" are protected.