By Amy E. Feldman

PHILADELPHIA (CBS) - Thinking of writing a negative on line review on a website like Yelp?

A dentist in Portland, Oregon sued a former patient whom he claims damaged his reputation by posting negative reviews about him on Yelp. Many are confused about freedom of speech and its limits – and the limits on trying to limit it. Here’s what you need to know.

While you have the right to freedom of speech, defamation – a false statement of fact that damages someone’s reputation – is not protected speech and you can be sued for it.

But stating your opinion – or a truthful statement of fact – is not defamation.

Suing or threatening to sue someone just for saying, or posting, a negative review about you even though you know it’s not defamation is what is called a SLAPP lawsuit – a strategic law against public participation. It is a lawsuit brought to silence you, and that’s not legal.

So, while you do have the right to your opinion, and you can’t face a lawsuit brought to silence you, in general the writing of nasty, negative, and hurtful reviews should be considered carefully. The Portland dentist is pursuing a defamation action, the patient is pursuing an anti-SLAPP lawsuit. And probably a new set of teeth.