The First Amendment to the United States Constitution protects the right to express one’s opinions without fear of defamation lawsuits or other punishment. If you had a bad experience at a local restaurant, you are free to post a negative review on Yelp, Google, or some other consumer-review site and tell the world exactly what you think of the place. The restaurant may not appreciate the effect of your review on its average “star rating,” but it won’t be able to sue you for defamation (not successfully, anyway) if all you did was express your constitutionally-protected opinions. But what are those, exactly?
Distinguishing opinions from statements of fact is not as simple as it sounds, and in many cases, judges and scholars will reach opposite conclusions. For example, a common accusation that gets thrown around a lot is “scam artist” or “scammer.” Is that a factual assertion or an opinion? It’s hard to say without knowing more context. Is the declarant using the term to accuse someone of being “grossly unfair” (an opinion) or is he saying that actual fraud is taking place? Suppose someone writes online that Gatorade’s marketing campaign is a “scam” because Gatorade doesn’t really quench thirst as well as plain water. Contrast that with a statement accusing a local accountant of scamming customers out of hundreds of dollars by manipulating their tax returns. To “scam” someone means different things in different contexts.