Sometimes, for various reasons, parties to a federal lawsuit will want to amend their pleadings. For example, a defendant may move to dismiss the plaintiff’s complaint for failure to state a claim on which relief can be granted. Rather than having the whole case thrown out, the plaintiff may seek to amend the complaint so that it does state a claim upon which relief can be granted. Similarly, the defendant may want to amend her answer to assert additional defenses or to fix ineffective...