Those in which there is an agreement to constitute, for a particular purpose, the relation of principal and surety, to which agreement the secured creditor is a party;
those in which there is a similar agreement between the principal and surety only, to which the creditor is a stranger;
those in which, without any such contract of suretyship, there is a primary and a secondary liability of two persons for one and the same debt, the debt being, as between the two, that of one of those persons only, and not equally of both, so that the other, if he should be compelled to pay it, would be entitled to reimbursement from the person by whom (as between the two) it ought to have been paid.[1]