Noting that the "marketplace of ideas" metaphor often used in the study of freedom of speech is drawn from classical economics, this paper cites J. Murray's definition of the concept as "the idea that citizens in a democracy are well served if opinions of all kinds, accurate or inaccurate, are freely circulated." The first section of the paper traces the historical development of the metaphor, beginning with an examination of the image of truth competing with falsehood that emerged in political argument in the Reformation and later became part of the political language of the American colonies. It then traces this image in the legal language of American courts, pointing out that it was first used in 1919 by a United States Supreme Court justice, who used it as an economic metaphor in a dissenting opinion. The second section of the paper examines the use of the economic metaphor in United States Supreme Court opinions, where it was held that when ideas compete for acceptance, free of regulation, audiences will accept the good (true) ideas and reject the bad (false) ones. The paper argues that Supreme Court justices have also used the metaphor to draw upon a whole structure of economic terms, concluding that although the image is composed of terms that suggest commitment to a laissez-faire principle, its expression as an economic analogy allows the justices to draw upon such concepts as fraud, regulated monopolies, and Gresham's law, which permits both flexibility in decision making and commitment to a shared value. (FL)