Heres is my explaination on the two forms of co-ownership;
Under a joint tenancy the principles of ‘totum tenet et nilhil tenet’ – “each holds everything and yet holds nothing” applies. Joint tenants are regarded as collectively the single owner, a single legal entity. Joint tenants individually hold nothing “but each entitled to the whole ”, however they do have rights exercisable against one another.
The right of survivorship (ius accrescendi) only operates in joint tenancy. When one joint tenants dies his interest will pass to the surviving joint tenants; s.184 LPA 1925. This process will continue until only one joint tenant remains. At this point he becomes the sole owner, independently entitled to the land.
A joint tenant cannot sever his interest by will under s.184 , his interest automatically passes to the surviving joint tenants, and they are under no duty to pay death duties to the deceased’s estate . The interest the surviving joint tenants receive “is only in the sense that on sale their share will be higher” .
Co-owners can avoid the rules of survivorship by serving their joint tenancy thus converting it into a tenancy in common. This only applies in equity; one cannot sever a legal joint tenancy – s.36 (2) LPA 1925.
Tenants in common are recognised as having undivided shares in the land.
A tenancy in common only requires the unity of possession, the right of survivorship does not exist. Thus one may leave his interest to another outside of the trust.
One may convert his joint tenancy to a tenancy in common by way of severance, which is permissible in equity under s.36 (2) LPA 1925 as amended by Sch. 2 TLATA 1996.