Defamation is the act of harming the reputation of another by making a false statement (written or oral) to another person. As with every charge, there are defenses that can be made to counter the charge. Defamation works on the premise that a person's good name has value and if that good name is destroyed, the person who destroys it should be made to pay.
The burden of proof in a defamation claim, in most cases, is on the plaintiff.
Truth of the statement
If the statement is true, there is no defamation. If someone is a convicted rapist, you can't defame that person by telling people that fact.
There Must be Harm
The plaintiff must prove that his or her good name has been harmed, in order for a charge of defamation to stand up. If you say someone is a "deadbeat" and no one believes it, there is no harm. On the other hand, if you say someone is a deadbeat, and a bank declines to give that person a loan, he or she has a case against you for defamation.
There Must be Communication
It must be proved that the statement was communicated. If you wrote something about someone and you did not send it to anyone or publish it, there is no defamation. Communication requires a receiver of the message as well as a sender.
If you can prove that the plaintiff consented to the statement, in an interview, for example, or in a written statement of consent, there is no defamation.
A common defense against defamation is privilege, or immunity. There are many types of privilege, but the most common are absolute privilege and qualified privilege. Absolute privilege is immunity from charge of defamation, even if the statement is malicious. Absolute privilege is most often claimed by legislators. The other common privilege is qualified privilege, which protects the press from defamation charges for written or spoken statements, unless they can be proved to be malicious.
If it can be shown that a statement was opinion, rather than a pronouncement of a fact, the statement may not be determined to be defamatory. Opinion as a defense depends on the context, including the stature and presumed knowledge of the person making the statement.