David Wootton (pictured), writing in the TLS of September 23, 2005 ("Oxbridge Model"), has an engaging account of the history of the terms "democracy" and "republic." He reviews a new book by John Dunn, Setting the People Free: The story of democracy, and in the course of it discusses the rise of these two words in political discourse. (Unfortunately, the review is not publicly available online at the TLS.)
Wootton notes that for the ancient Greeks, the word democracy needed to be
"fitted into a sixfold classification of types of government: monarchy and tyranny; aristocracy and oligarchy; democracy or polity and democracy or mob rule. The problem with 'democracy' was that it wasn't clear if it was the name for a good form of government, a bad form of government, or a paired set of good and bad forms of government ... From the very beginning the word was slippery."
The word "republic," he goes on, comes from the Romans. The Romans, Wootton says, "had no word for democracy," so they paraphrased "the concept into Latin as government by the people." This led them to introduce a new term, res publica, which "included the three good forms of government and excluded the three bad forms." Then, in Renaissance Florence, at the time of Savonarola, a "remarkable linguistic revolution took place: the only real republic, it was argued, was a popular government ... Monarchies were always tyrannies; aristocracies were always oligarchies, which were themselves forms of tyranny."
Fast forward to the American and French revolutions. They were carried out, Wootton tells us, in the name not of democracy, but of republicanism. But anyone who understood this language "could see that the world 'republic' occupied an intellectual space previously occupied by 'democracy'. Just as democracy had been a slippery term, so too was its substitute, republic, but the direction of slippage was now different: there was an alternative modern definition of republic that was anything that was not a monarchy." Quoting Robespierre, "democratic or republic, these two words are synonymous." It is not until this age of Enlightenment revolutions that the difference often ascribed to democracy versus republic takes hold - the idea of a republic as a representative democracy, rather than direct Greek democracy. And yet, in another peculiar linguistic twist, after the French revolution, American began calling themselves "democrats" precisely in order to distinguish themselves from the French revolutionaries who, pace Robespierre, called themselves republicans.
Thus, says Wootton, the real beginning of modern democratic theory "lies not in ancient Athens but in ... the written constitution, the separation of powers. And these ideas date to ... the English Civil War."