Cause is the reason why a party obligates himself.
A party may be obligated by a promise when he knew or should have known that the promise would induce the other party to rely on it to his detriment and the other party was reasonable in so relying. Recovery may be limited to the expenses incurred or the damages suffered as a result of the promisee's reliance on the promise. Reliance on a gratuitous promise made without required formalities is not reasonable.