nemo dat quod non habet
[Latin: no one can give what he has not got]
The basic rule that a person who does not own property (e.g. a thief) cannot confer it on another except with the true owner's authority (i.e. as his agent). Exceptions to this rule include sales under statutory powers and cases in which the doctrine of estoppel prevents the true owner from denying the authority of the seller to sell.