How does a joint tenancy in common work?

In his decision, the trial judge referred to the following principle of law taken from Williams v. Hensman.[3] A joint tenancy may be severed in three ways: in the first place, an act of any one of the persons interested operating upon his own share may create a severance as to that share. The right of each joint-tenant is a right by survivorship only in the event of no severance having taken place of the share which is claimed under the jus accrescendi. Each one is at liberty to dispose of his own interest in such manner as to sever it from the joint fund -- losing, of course, at the same time, his own right of survivorship. Secondly, a joint tenancy may be severed by mutual agreement. And, in the third place, there may be a severance by any course of dealings sufficient to intimate that the interests of all were mutually treated as constituting a tenancy in common. When the severance depends on an inference of this kind without any express act of severance, it will not suffice to rely on an intention, with respect to the particular share, declared only behind the backs of the other persons interested.