Petition is a term given to the first filing that opens a lawsuit, also called a complaint. You can often amend a petition if you follow proper procedures. In a legal case, the only signature a petition requires is that of the person or attorney filing it.
A civil lawsuit opens when someone files a complaint and often ends with the judgment. That initial document sets out the basic outline of the lawsuit, the who-did-what facts as well as an overview of the injuries or damage caused. If you don't know all the facts when the last moment comes to file, you can file now and amend later.
Amending Before Response
It takes at least two to argue, and the person you are suing also gets her day in court. She has a set period of time, after you give her the legal documents, to file her own papers with the court denying the charges. If you learn of new, relevant facts that should go in your petition, you can amend it without permission before the other side responds. Depending on court rules, you either file a whole new complaint containing the new facts, termed an amended complaint, or else a document that lists the amendments. The other party responds only to the amended version of the petition, not the original one.
Amending After Response
When you learn new facts after the other side answers your petition, the process of amendment becomes more complicated. Your first step is to ask the other party to agree that you can file an amended complaint. If she does, you proceed in the same way you would for an amendment before a response. If not, you must ask the court's permission and convince the judge that allowing an amended complaint is fair and just. Generally, your papers explain why you did not and could not have learned of the newly discovered facts earlier.
Amending to Conform to Proof
The opening documents each side files are intended to set the boundaries of the issues to be raised in trial. However, if other, related issues arise during trial, the court often permits an amendment to change your petition to include the new issues, called an amendment to conform to proof.
Much of the stickiness around amendments stems from the time limits on filing a complaint. Laws called statutes of limitation set time periods in which you must file a complaint about a problem or you can no longer sue. For example, if a doctor cuts off the wrong leg in your surgical procedure, you have a set period of time from that date to bring a malpractice action. If new facts come to your attention after that limitations period has passed, it will be too late to include new claims based on those facts in your lawsuit unless they relate back to the initial filing date. Generally, judges hold that amendments relate back to the initial date if they are part of the same set of circumstances that you described in your original petition.