grantor may have a future possessory interest. Executory interests are subject to the rule against perpetuities, which disqualifies any interest that can vest more than twenty-one years after the death of every party who was living at the time the interest was created. However, if all of the potential vesting beneficiaries are named, the rule will never be violated. Thus, a property can not be conveyed "to A and her heirs, but if alcohol is consumed on the property, to B and his heirs". Because A's heirs may hew to the condition for generations, causing a violation centuries after the condition was set down and creating chaos in efforts to shift title to the appropriate heirs of B. Third party beneficiaries of executory interests cannot alienate them, since the interests are contingent upon a condition subsequent, so the interest is not guaranteed to vest. References See also Executory contract Executory interest Rule against perpetuities Real property law Wills and trusts