Rule 15.Amended and supplemental pleadings

Rule 15(a) gives a party one amendment as a matter of right -- at any time before a responsive pleading is served, or, for a pleading that gets no responsive pleading and hasn't yet been placed on the trial calendar, within 20 days after it was served. Beyond that, amendment requires either leave of court or the adverse party's written consent, and leave must be freely given when justice so requires. A party facing an amended pleading has to respond within whatever time remained for the original pleading, or within 10 days after the amended pleading is served, whichever is longer, unless the court orders otherwise. Rule 15(aa) requires the amending party to plainly indicate, in the amended pleading itself, how it differs from the pleading it amends.

Rule 15(b) addresses issues that come up at trial without having been pleaded. If the parties try an unpleaded issue by express or implied consent, it's treated in every respect as if it had been raised in the pleadings, and the pleadings can be amended -- even after judgment -- to match the evidence, though failing to amend doesn't change the outcome of the trial on that issue. If a party objects that evidence falls outside the pleadings, the court can allow amendment and should do so freely when it would help present the case on the merits and the objecting party can't show the new evidence would prejudice its case; the court may grant a continuance to let the objecting party respond to the new evidence.

Rule 15(c) sets three routes by which an amendment relates back to the date of the original pleading -- important because that earlier date can save a claim from a statute of limitations: relation back is allowed by the law supplying the statute of limitations for the action; the amended claim or defense arose from the same conduct, transaction, or occurrence set out (or attempted to be set out) in the original pleading; or the amendment changes the party being sued, if the conduct test in the second route is met and, within the time allowed for serving the summons and complaint, the newly named party received enough notice of the action that it won't be prejudiced in defending on the merits, and knew or should have known that, but for a mistake about identity, the action would have been brought against it.

Rule 15(d) lets a party, on motion and on just terms, serve a supplemental pleading setting out transactions, occurrences, or events that happened after the date of the pleading being supplemented -- even if the original pleading was itself defective in stating a claim or defense. The court can order the adverse party to respond to the supplemental pleading and set the time for doing so.