принцип взаимности(Article 1308 of the Civil Code expresses what is known in law as the principle of mutuality of contracts. It provides that "the contract must bind both the contracting parties; its validity or compliance cannot be left to the will of one of them." This binding effect of a contract on both parties is based on the principle that the obligations arising from the contracts have the force of law between the contracting parties, and there must be mutuality between them based essentially on their equality under which it is repugnant to have one party bound by the contract while leaving the other free therefrom. The ultimate purpose is to render void a contract containing a condition which makes its fulfillment dependent solely upon the uncontrolled will of one of the contracting parties. lawphil.netAlexander Demidov)
