The illegality of a contract or sale may result either from the illegality of the promise or from the illegality of the consideration given for the promise. A promise to do an illegal thing for a legal consideration is unenforceable,66 and equally so is a promise to do a legal thing for an illegal consideration.67 If the agreement is bilateral and the promise on either side is unlawful, both promises are unenforceable; for one promise is itself unlawful and the other is given for unlawful consideration. If an illegal contract has been partly executed, the parties are in effect left as they stand, for all relief for non-performance of the rest of the obligation is denied. Therefore, a seller cannot recover possession of goods illegally sold on a conditional sale, though the condition has been broken.68