From Florida Legal Wiki
An “affirmative defense” is any defense that assumes the complaint or charges to be correct but raises other facts that, if true, would establish a valid excuse or justification or a right to engage in the conduct in question. An affirmative defense does not concern itself with the elements of the offense at all; it concedes them. In effect, an affirmative defense says, “Yes, I did it, but I had a good reason.” State v. Cohen, 568 So.2d 49, 51-52 (Fla. 1990). Stated differently, an affirmative defense is any matter that avoids the action and that, under applicable law, the plaintiff is not bound to prove initially but the defendant must affirmatively establish. Langford v. McCormick, 552 So.2d 964, 967 (Fla. 1st DCA 1989).
The Florida Rules of Civil Procedure authorize affirmative defenses to be raised pursuant to Rule 1.110(d), General Rules of Pleading, and lists several affirmative defenses. The list is outdated, as several of the affirmative defenses have been rendered moot by changes in the law, but serves as a useful starting point:
- Accord and Satisfaction
- Arbitration and Award
- Assumption of Risk
- Contributory Negligence
- Discharge in Bankruptcy
- Failure of Consideration
- Injury by Fellow Servant
- Res Judicata
- Statute of Frauds
- Statute of Limitations
The above list is not comprehensive and any matter constituting an affirmative defense must be pled. Accordingly, some Courts have also recognized the following as distinct affirmative defenses:
- Collateral Estoppel
- Failure to Mitigate
- Undue Influence
- Want of Consideration
 Pleading Requirements
Certainty is required when pleading affirmative defenses and pleading conclusions of law unsupported by allegations of ultimate fact is legally insufficient. Bliss v. Carmona, 418 So.2d 1017 (Fla. 3d DCA 1982). Allegations in an Answer that purport to be affirmative defenses, but which are nothing more than denials or conclusions of law must be stricken. Wiggins v. Protmay, 430 So.2d 541 (Fla. 1st DCA 1983).
Affirmative defenses are waived if not pled. Jojo's Clubhouse, Inc. v. DBR Asset Mgmt., Inc., 860 So.2d 503, 504 (Fla. 4th DCA 2003), citing See Wolowitz v. Thoroughbred Motors, Inc., 765 So.2d 920, 923 (Fla. 2d DCA 2000); and Goldberger v. Regency Highland Condo. Ass'n, 452 So.2d 583, 585 (Fla. 4th DCA 1984).
 Striking Affirmative Defenses
Often a Defendant will assert affirmative defenses without any supporting factual allegations. Such affirmative defenses are improper since an affirmative defense is a pleading and must be supported by factual allegations like the allegations in a Complaint. The proper response to such unsupported affirmative defenses is a Motion for More Definite Statement per Fla. R. Civ. P. 1.140(e). If, following a hearing and Order of the Court, factual support is not provided, the challenged affirmative defense may be stricken.
 Responding to Affirmative Defenses
Generally, no response is necessary. "When affirmative defenses are raised the facts pleaded thereby are deemed denied" Falick v. Sun N Sea, Inc., 81 So.2d 749, 750 (Fla. 1955). "A reply is required only if the pleader wishes to avoid the affirmative defense." Hertz Commercial Leasing Corp. v. Seebeck, 399 So.2d 1110, 1111 (Fla. 5th DCA 1981).
Once an affirmative defense is raised, the Plaintiff has the burden of either disproving it or establishing the legal insufficiency of the affirmative defense. Florida Dept. of Agric. v. Go Bungee, Inc., 678 So.2d 920, 921 (Fla. 5th DCA 1996), citing Wilson v. Pruette, 422 So.2d 351, 352 (Fla. 2d DCA 1982).
A Complaint will not be dismissed based on an affirmative defense except where the facts that prove the affirmative defense appear on the face of the Complaint.