pactum constitutae pecuniae

PACTUM CONSTITUTAE PECUNIAE, civil law. An agreement by which a person 
appointed to his creditor, a certain day, or a certain time, at which he 
promised to pay; or it maybe defined, simply. an agreement by which a person 
promises a creditor to pay him. 
     2. When a person by this pact promises his own creditor to pay him, 
there arises a new obligation which does not destroy the former by which he 
was already bound, but which is accessory to it; and by this multiplicity of 
obligations the right of the creditor is strengthened. Poth. Ob. Pt. 2, c. 
6, s. 9. 
     3. There is a striking conformity between the pactum constitutae 
pecuniae, as above defined, and our indebitatus assumpsit. The pactum 
constitutae pecuniae was a promise to pay a subsisting debt whether natural 
or civil; made in such a manner as not to extinguish the preceding debt, and 
introduced by the praetor to obviate some formal difficulties. The action of 
indebitatus assumpsit was brought upon a promise for the payment of a debt, 
it was not subject to the wager of law and other technical difficulties of 
the regular action of debt; but by such promise, the right to the action of 
debt was not extinguished nor varied. 4 Rep. 91 to 95; see 1 H. Bl. 550 to 
655; Doug. 6, 7; 3 Wood. 168, 169, n. c; 1 Vin. Abr. 270; Bro. Abr. Action 
sur le case, pl. 7, 69, 72; Fitzh. N. B. 94, A, n. a, 145 G; 1 New Rep. 295; 
Bl. Rep. 850; 1 Chit. Pl. 89; Toull. Dr. Civ. Fr. liv. 3, t. 3, c. 4, u. 
388, 396.