What are defenses to defamation?
There are certain defenses to defamation. For one, truth is an absolute defense, as well as consent. Second, certain statements, defamatory or not, are privileged - these include statements made on the floor of the legislature, statements made by sitting judges, or arguments made by lawyers in court. Furthermore, “opinion” is another defense to defamation in many jurisdictions: statements of opinion (as opposed to fact) are protected (the question then becomes, was the statement opinion or fact?). Moreover, you are allowed to make fair comments on matters of public concern, such as “I believe Barry Bonds took steroids,” which is protected whether the allegation is true or not.
Finally, if the person being defamed is a public figure, the person being defamed must also prove that the statement was made with actual malice, i.e., the person making the statement not only knew it was false, but made it in reckless disregard of the truth. People considered public figures include any person who receives frequent media attention, or is well-known in a particular area.