A more thorough explanation:

Commercial speech is a type of speech that promotes some kind of business or commerce. It is not as protected under the First Amendment as other types of speech. The government can regulate commercial speech if it meets certain criteria.

1. The speech must concern lawful activity and not be misleading.
2. The government must have a substantial interest in regulating the speech.
3. The regulation must directly advance the government's interest.
4. The regulation must not be more extensive than necessary to serve the government's interest.

In Linmark Associates v. Township of Willingboro, a township tried to prevent residents from placing "For Sale" or "Sold" signs on their lawns. The court ruled that preventing the flow of truthful information was more extensive than necessary to serve the township's interest of preventing further neighborhood members from leaving. Therefore, the township could not regulate this type of commercial speech.

Another example is Zauderer v. Office of Disc. Counsel, where the Supreme Court held that a state can require an advertiser to disclose certain information as long as it is reasonably related to the state's interest in preventing deception of consumers. This means that the state can compel commercial speech in certain situations.

These examples illustrate how the government can regulate or compel commercial speech if it meets certain criteria. The government's interest must be substantial, and the regulation must not be more extensive than necessary to serve that interest.