Four unities

The four unities is a concept in the common law of real property describing conditions that must exist in order for certain kinds of property interests to be created. Specifically, in order for two or more people to own property as joint tenants with right of survivorship, or for a married couple to own property as tenants by the entirety, they must have the following unities:

*Time = interest must be acquired by both tenants at the same time
**At common law, the "time" requirement could be satisfied only by using a "straw man" to create a joint tenancy. The party creating the joint tenancy would have to convey title to a fictional straw man, who would then transfer title to the two parties as joint tenants.
*Title = both tenants must have the same title to the property in the deed
*Interest = both tenants must have the same interest in the property
**This means that the joint tenants must have the same type of interest, and the interest must run for the same duration. For example, if X and Y create a joint tenancy, both X and Y's interests must be in Fee Simple Absolute. If X has an FSA and Y has a life estate, there is no unity of "interest."
*Possession = both tenants must have the right to possess the whole property

*Marriage = In order for there to be a tenancy by the entirety this fifth unity must be present. Marriage combined with the preceding four unities creates a tenancy by the entirety. A tenancy by the entirety gives rise to certain legal rights, such as rights of survivors, when one spouse is deceased that interest automatically passes to the surviving spouse.

If any of the four unities is broken and it is not a tenancy by the entirety, the ownership reverts to a tenancy in common.