29. The obligation is personal in another sense, as when the obligor binds himself to do a thing, and he provides his heirs and executors shall not be bound; as, for example, when he promises to pay a certain sum yearly during his life, and the payment is to cease at his death.

30. The obligation is real when real estate, and not the person, is liable to the obligee for the performance. A familiar example will explain this: when an estate owes an easement, as a right of way, it is the thing and not the owner who owes the easement. Another instance occurs when a person buys an estate which has been mortgaged, subject to the mortgage, he is not liable for the debt, though his estate is. In these cases the owner has an interest only because he is seised of the servient estate, or the mortgaged premises, and he may discharge himself by abandoning or parting with the property.

31. The obligation is both personal and real when the obligor has bound himself, and pledged his estate for the fulfilment of his obligation.