Rationale for freedom of expression based on an analogy of communication to goods in the economic marketplace. The theory holds that the truth arises out of the competition of ideas in an open market.

The rationale is articulated in U.S. Supreme Court case law in the case Abrams v. U.S. 250 US 616, 1919. The dissenting opinion here written by Justice Oliver Wendell Holmes and joined by Justice Louis Brandeis is, according to the U.S. State Department, "widely recognized as the starting point in modern judicial concern for free expression." (Source) Holmes explains in this famous dissent: "Persecution for the expression of opinions seems to me perfectly logical. If you have no doubt of your premises or your power and want a certain result with all your heart you naturally express your wishes in law and sweep away all opposition.... But when men have realized that time has upset many fighting faiths, they may come to believe even more than they believe the very foundations of their own conduct that the ultimate good desired is better reached by free trade in ideas -- that the best test of truth is the power of the thought to get itself accepted in the competition of the market, and that truth is the only ground upon which their wishes safely can be carried out. That at any rate is the theory of our Constitution."

The marketplace of ideas is also a theory that claims that we ought to be exposed to a wide array of ideas and thoughts in order to be able to pick the idea that best suits us. If the marketplace of ideas is limited, humans can not make well informed decisions and communities (state, national and/or global) are directly impacted.