Rows usually make good reading. Writers often encourage them. Adam Smith saw writers as competitive and jealous - each "often avowedly, and almost always secretly, the mortal enemy of the reputation of every other". Sometimes Adam Smith was right.

For the past six years I've been writing Scotland's Books, the first single volume to present the full history of 15 centuries of Scottish literature. The book is published by Penguin this week. Work on it has taught me how important it is to see Scotland's languages and cultures as inter-related, rather than isolated from each other. Even now there are discoveries to be made - not least in the Scottish Enlightenment.

That Scottish Enlightenment was not just a pure-minded, calm search for enlightened rationality. It progressed through literary rows. Gaelic, Latin, Scots and English were all involved. There were prose rows over Britishness and democracy, the place of religion, the use of the Scots tongue. There were poetic rows over the ancient poems of Ossian: a translated Gaelic masterwork or a cooked-up imperial fake? As noisy as any was the row over Scottish drama.

Scotland, the old story goes, was a land where the Kirk had extinguished theatre. The new story is more nuanced than that. During the Renaissance, one of the Kirk's first Moderators was a playwright whose European reputation was greater than that of Shakespeare. His name was George Buchanan, and there was fresh interest in his work during the Scottish Enlightenment.

Buchanan had written in Latin, one of the great languages of Scottish literature. The study of the Classics, like the study of philosophy, underpinned the Scottish Enlightenment. But the language of self-conscious modernity was English. France had Racine, England had Shakespeare. Why shouldn't Scotland have an English-language dramatist to match?

Certainly there were Scottish theatre-haters. In early eighteenth-century Glasgow, the university principal suppressed student theatricals as depraved. In Edinburgh a few decades earlier, the flamboyant Thomas Sydserf had been assaulted at sword-point by a gang eager to stop a rehearsal at "his hous in the Canongate, quher he keeps his theater for acteing his playes". Theatre in Scotland could be life-threatening. Some Presbyterians saw it as encouraging wickedness.

Yet others did not. In 1750 William Tait translated into English a play by Buchanan, hinting how such drama might bring Kirk and theatre together. Four years later, the moderate Rev Alexander Carlyle wrote a theatrical prologue for performance in Edinburgh, hoping for a time when "happier Bards shall rise, and future Shakespears light our northern skies!"

Some Scots sought to extinguish theatre. Others longed for a Scottish Shakespeare. Conditions were ripe for confrontation. What provoked it was a play by a Kirk minister.

The Rev John Home was a trained Classicist - his first play was set in ancient Greece. In London, the great man of the theatre, David Garrick, turned it down, along with Home's second tragedy, Douglas.

First performed in Edinburgh in 1756, Douglas was an English-language play based on a Scots ballad and hinting Highland culture might attract Lowland writers. This led to the internationally influential vogue for the Ossianic "Gaelic" poems which took off in the following decade, and initiated the worldwide Romantic fascination with the Scottish Highlands. "My heart's in the Highlands," wrote the theatre-loving Robert Burns. The first play he saw was Home's Douglas.

Douglas celebrates northern heroism, Highland mountains, and the tragic fates of a mother and her long-lost son. Staged just a decade after Culloden, with its hero from "the Grampian hills", it made Highland culture sympathetically attractive even to loyal Hanoverian Lowlanders who had opposed the Jacobite rebels. It encouraged the sort of interaction between Highland and Lowland culture which powers some of the best works of Burns and Scott, James Hogg and Susan Ferrier.

Appealing to women as well as men, Douglas was elegant, sophisticated and ambitious. Performed in 1756 at the Canongate Theatre in Edinburgh, this verse-play was hailed as a milestone in Scottish drama. It also caused a scandal, which helped make it by far the most famous play of the Scottish Enlightenment.

In the row over Douglas, liberal ministers argued with their less liberal, play-hating brethren. Mocking the play-haters, Alexander Carlyle issued anonymously a spoof Argument to prove that the tragedy of Douglas ought to be Publickly burnt by the hands of the Hangman.

More solemnly, the philosopher Rev Adam Ferguson, in The Morality of Stage-Plays Seriously Considered, thought dramas might be good for commerce as well as virtue. David Hume, a relative of John Home and a man unlikely to side with Kirk hard-liners, thought Douglas better than Shakespeare; Hume, Adam Ferguson and other eminent Scots acted in the play's rehearsals.

The cultural excitement around Douglas in Edinburgh in 1756-7 is hard to over-state. "Whaur's yer Wullie Shakespeare noo?" one audience member is reputed to have called out when the play was performed. Praise for Douglas was sometimes daft, but accompanied acclaim for Enlightenment values. Today there are major collections of documents and pro- and anti-Douglas pamphlets in the National Library of Scotland and in the Folger Library, Washington. Yet no writing captures the intellectual and patriotic ferment better than the manuscript prologue now in St Andrews University Library. I came across this while researching Scotland's Books, where it is published in full for the first time.

The prologue, dated in manuscript to the day of Douglas's first performance, is worth quoting for its clear ambition, and its willingness to see Scottish drama in a broad historical and international light. The writer wants a Scottish theatre which can rival the best in the world:

"Foretold by Carlyle, now the time is come - When Scotia bears the Palm from Greece and Rome, When the learn'd Youth, Wits of the present Age, No more need form their Taste on the translated page, When Beauxs and Belles old Shakespear shall deride, And Bucks and Bloods cast Rochester aside . . ."

Wanting a theatre so alluring and exciting that even Shakespeare and the erotic poetry of the Earl of Rochester will pall beside it, this prologue may be a little risible. In the end, Douglas, for all its eighteenth-century importance, now sounds too designed for elocution teachers, many of whom loved it.

Yet without Douglas's ambition, its capacity to provoke and even to realign elements in Scottish culture and public opinion, both the trajectory of the Scottish Enlightenment and the course of Scottish theatre would have been different.

Though the "new" prologue has lain unpublished for a quarter of a millennium, its combination of international ambition and clear Scottish confidence emanates from the heart of the Scottish Enlightenment. Its rediscovery is a wink from a remarkable cultural moment. In its way, that wink signals the unpredictable excitement of the greatest Scottish literature - from the Latin and Gaelic poetry of St Columba's Iona to the best Scots and English work produced today by the National Theatre of Scotland.

  • Robert Crawford's Scotland's Books: The Penguin History of Scottish Literature, is published this week at £15.99.