A determinable estate may end early automatically upon the happening of the limiting event.
It relies on a duration without a condition happening. Words of duration are like: "until", "during", "as long as", or "while". The words of limitation will usually be in the original conveyance.
It gives the grantee a possessory estate in fee simple determinable.
If the future interest is retained by the grantor, it gives him a possibility of reverter.
If the future interest is given to another grantee, it gives that person an executory interest.