Executory interest: a future interest in a third party which is not a remainder and that cuts the prior estate short upon the happening of

a stated event or condition
-springing executory interest: divests the interest of grantor or follows a gap in possession in which estate

reverts to grantor; examples: “O to A for life and one year later to B and heirs” or “O to A if and when he marries X”
-shifting executory

interest: divests the interest of grantee by cutting short prior estate created in same conveyance; examples: “O to A and heirs, but if B

returns from Paris, then to B” or “O to A for life, then to B and heirs, but if B ever farms the land, then to C and heirs”