The Agreement of Purchase and Sale will have many terms and conditions that both parties negotiate and finally agree to before finalizing a deal. If one party wants to make any changes after the deal has been accepted, it must be done through an amendment to the agreement, a separate document that all parties sign in agreement to the changes. Sometimes a clause is added to the original deal that gives one party, buyer or seller, the right to change the closing date. The clause will be written in a way that dictates whether or not they can do this unilaterally, by simply serving notice to the other party. On the other hand, it may say that the date can only be changed by mutual consent, in which case an amendment must be generated and all parties must agree. When an issue arises and changes are requested, they can be made the same way, through an amendment to the agreement, and no clause is needed in the original Agreement of Purchase and Sale.