No one can be made liable on a contract who is not a party to it. A and B have no power to make a private agreement which can compel C to do something. Suppose A and B had agreed that B was to do something for C. Can C sue B if B does not do what he has agreed to? Here the contract has been specifically made for C's benefit. In this country the general rule is that a third person may enforce a promise made for his benefit even if he has furnished no consideration for the promise. If, after A and B have made a contract, can they both agree with X that he shall take B's place? This is permitted, and is really a new contract. But can A, without obtaining B's permission, give his (A's) rights to X and compel B to deal with X? In most kinds of transactions this is permitted. But A would still be liable to B if X did not do what A had agreed to do.