… is from page 368 of William Leggett ‘s February 11, 1837, Plaindealer essay, “Free Trade, Taxes, and Subsidies,” as this essay is reprinted and titled in Democratick Editorials , Lawrence H. White, ed. (Indianapolis: Liberty Fund, 1984):
It is a mistake to say that theoretick free trade consists in the equality of duties. It consists in levying no duties at all. It consists in leaving the parties to trade – the buyer and seller -perfectly unrestrained by the conditions of a third party.