An executory interest is an interest in a grantee following a determinable estate or an estate subject to an executory limitation.
An executory interest automatically takes effect upon the happening of the condition. Its distinguishing characteristic from a contingent interest is that it divests other interests early.
Executory interests can be shifting or springing.
A shifting executory interest divests an estate in another grantee.
e.g. A to B, but if C graduates, to C. C has a shifting executory interest.
A springing executory interest divests an estate in a grantor.
e.g. A to C, if C graduates. C has a springing executory interest.