According to the legal information site HG.org, a person is qualified to sue for slander if he has proof of being defamed verbally and can show that he has suffered damages as a result. Defamation is a false statement about a person that leads the subject to suffer injury, such as financially, professionally or personally.
According to HG.org, the slander must include either a false statement of fact or an opinion that is designed to intentionally inflict harm. Negative statements that are true or negative opinions that are not made with malignant intent are protected by free speech and typically do not entitle a person to sue for slander.
In addition to meeting those requirements, the statement must cause actual, quantifiable harm to the subject. Statements that are false but do not harm the subject are not actionable. For example, the loss of a job resulting from false statements qualifies a person to sue. The attorneys at HG.org also state that a person needs proof to pursue a suit for slander. Proof can include witness statements, audio recordings or another type of record of the slanderous statement.
According to FindLaw, statements that occur during a judicial or legislative inquiry, statements made between spouses and statements made as required by law are immune to a defamation suit. Additionally, standards for public figures and nonpublic figures for proving falsity vary.