New York Consolidated Laws, Civil Practice Law and Rules - CVP § 3018. Responsive pleadings

(a) Denials. A party shall deny those statements known or believed by him to be untrue. He shall specify those statements as to the truth of which he lacks knowledge or information sufficient to form a belief and this shall have the effect of a denial. All other statements of a pleading are deemed admitted, except that where no responsive pleading is permitted they are deemed denied or avoided.

(b) Affirmative defenses. A party shall plead all matters which if not pleaded would be likely to take the adverse party by surprise or would raise issues of fact not appearing on the face of a prior pleading such as arbitration and award, collateral estoppel, culpable conduct claimed in diminution of damages as set forth in article fourteen-A, discharge in bankruptcy, facts showing illegality either by statute or common law, fraud, infancy or other disability of the party defending, payment, release, res judicata, statute of frauds, or statute of limitation. The application of this subdivision shall not be confined to the instances enumerated.