In ordinary circumstances the buyer himself will be responsible for the price, but payment by a third party (either on behalf of the debtor, or as surety or co-debtor) also discharges the obligation.

In the first instance the co-signer's obligation may be in the nature of a guaranty, while in the second instance the co-signer's obligation might be described as that of a co-debtor.

This case also concerned a joint and several promissory note, to which the defendant pleaded that the co-debtor had been released by deed on making a composition with the creditors, but the deed contained a proviso that it should not operate to prejudice the rights of others.

It is to prevent circuity of action, inasmuch as if the released debtor were still liable to an action for contribution by his co-debtor (who had been sued and had paid), he would not in fact be released:North v. Wakefield, 13 Q.B.

Where you find those two provisions you construe the document, not as a release, but merely as an undertaking not to sue a particular individual, and the result is that the right to proceed against the co-debtor is reserved and can be put in force against him.

Whenever you can find from the terms of the document an agreement for the reservation of rights against the co-debtor, then, I agree, the document cannot be construed as an accord and satisfaction of the joint debt, and, therefore, as a release of the co-debtor.