The first paragraph of Article 45 of Contract Law provides that the parties have the freedom to agree to attach conditions on the validity of the contract. Conditions are characterized by intentionality, futurity, probability and legality. Conditions on the entry into effect and conditions on dissolution are two types of conditions stipulated by positive law in our country. A contract with collateral conditions on its entry into effect shall become effective upon the fulfillment of the conditions. A contract with collateral conditions on its dissolution shall lose its validity upon the fulfillment of the conditions. However, for the protection of public welfare or private benefits, the family law on non-property legal acts, bill behavior, consensus on transfer of real estate and other legal acts shall not be conditional. During the pending period, the parties shall act in good faith in order to respect the expectant right of the relative person. Based on the principle of honesty and good faith, the second paragraph of Article 45 of Contract Law establishes the fictitious rules on conditional achievement or non achievement; however, this provision is slightly rigid. In accordance with the provisions of positive law, the achievement of conditions has no retroactive effect; the provision is arbitrary norm.