Federal Rule of Civil Procedure 15(a) provides that a 'party may amend the party's pleading once as a matter of course at any time before a responsive pleading is served ....' FED. R. CIV. P. 15(a). Once a responsive pleading is filed, 'a party may amend the party's pleading only by leave of the court or by written consent of the adverse party; and leave shall be freely given when justice so requires'; see also Foman v. Davis, 371 U.S. 178, 182, 9 L. Ed. 2d 222, 83 S. Ct. 227 (1962).
Fed.R.Civ.P. 15(a) provides that leave to amend an answer should be freely given when justice requires. The Federal Rules clearly favor a liberal attitude towards amendments. The purpose of a permissive attitude is to encourage decision of the case on the merits by allowing parties to present the real issues of the case. See, United States v. E. B. Hougham, 364 U.S. 310, 317, 81 S. Ct. 13, 5 L. Ed. 2d 8 (1960).
A court may deny a request to amend if it bases such denial upon a valid ground. Among the reasons commonly cited for denying permission to amend ...