The First Amendment generally protects all sorts of speech, whether about politics, science, morality, or the details of daily life. But in certain situations, First Amendment law draws a line between speech on matters of "public concern" and speech on matters of "private concern"; for instance,
- In libel cases brought by private figures based on public-concern speech, the plaintiff must show "actual malice" (knowing or reckless falsehood) to recover presumed or punitive damages. In libel cases brought based on private-concern speech, the plaintiff need only show negligence (to oversimplify slightly). See Dun & Bradstreet v. Greenmoss Builders.
- Speech on matters of public concern is generally fully protected against intentional infliction of emotional distress claims (as in Snyder v. Phelps). Speech on matters of private concern, including true statements and statements of opinion, might be subject to such claims.
- Disclosure of "non-newsworthy" private facts might lead to tort liability under the disclosure of private facts tort. The newsworthy/non-newsworthy line likely tracks the public/private concern line.
- Some courts have allowed (wrongly, I think) injunctions against "harassing" speech, again potentially including true statements and statements of opinion, when the speech is supposedly on a matter of "private concern."
- The Court has held that the First Amendment generally doesn't restrict government employers' retaliating against their employees for speech on matters of private concern. See Connick v. Myers.
- Many states have so-called "anti-SLAPP" statutes that let defendants move to promptly dismiss speech-based lawsuits against them, and generally get attorney fees if they prevail. But those statutes are generally limited to speech on matters of public concern (though some of those statutes define that term in specific ways).
