Definition of Four unities:
Legal requirements for the creation of a joint-tenancy agreement. They are (1) Unity of interest: interests of all joint-tenants must be identical in duration, extent, and nature. (2) Unity of possession: each joint-tenant must have undivided share of the property simultaneously with other joint-tenants, and no joint-tenant can have exclusive right to possess the whole property. (3) Unity of time: interest of all joint-tenants must vest at the same time and for the same period. (4) Unity of title: all joint-tenants must have an equal title to the property, created by the same instrument.
Meaning of Four unities & Four unities Definition