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, these four unities must be met 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. Some jurisdictions may require additional unities.

The four unities

Unity of time 

Interest must be acquired by both tenants at the same time.

In 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 straw man, who would then transfer title to the two parties as joint tenants.

Unity of title 

The interests held by the co-owners must arise out of the same instrument.

Unity of 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, for example, X has a fee simple absolute and Y has a life estate, there is no unity of interest.

Unity of possession 

Both tenants must have the right to possess the whole property.

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

A fifth unity

Unity of 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.

A sixth unity

Unity of unison 

In order for the parties to be united, they must be in unison. This has been criticised by the Law Commission in their 283rd report, entitled 'Unity in Leaseholds'.