Writers who draw creative inspiration and subject matter from history for poem, novel, play or film have a freedom denied historians to simplify the story, transpose characters and events, and sharpen conflicts within and between characters.
The purpose is entertainment, instruction, and to convey truth in a metaphysical sense rather than literally. Keats expressed this in his Ode on a Grecian Urn: Beauty is truth, truth beauty, that is all/Ye know on earth, and all ye need to know.
Those who know the particular history may spot the divergences. Among the vast majority who do not, some may be stimulated into reading up more, whether the subject is Troy, the Crusades, William Wallace (Braveheart) or Michael Collins.
Brian Friel is the contemporary Irish dramatist who has probed most deeply into the meaning of Irish history and the conflict and interaction between the different traditions.
The Home Place, on the relationship between the Anglo-Irish and the surrounding population in Donegal against the backdrop of Lord Leitrim's assassination, was excellently performed at the Gate Theatre earlier this year, before moving on to London.
The Times box office service on Thursday definitely pushed poetic licence too far, when it claimed that "the play is set in Ireland in 1878, at the beginning of Home Rule".
While characters in a historical drama are confined to a particular space and time and largely the mindsets that go with the period, the audience knows the sequel.
Friel's plays were written, not only during the Troubles, but against the backdrop, however chequered, of an independent Ireland.
One of his most powerful plays, Translations, takes as its subject the Ordnance Survey conducted between the 1820s and 1840s in pre-Famine Ireland, focusing particularly on the authentication of placenames, still a live topic today.
The survey is dramatised as a clumsily and insensitively conducted imperial project, speeding the process of anglicisation, which the governing class saw as the answer to Ireland's problems, including consolidation of an unpopular Union.
Local assistance was called for, people who could act as interpreters. Owen, the son of Hugh, who went away to make money in Dublin, is portrayed as venal, or, in the words of Séamus Deane, as a man with "the intimacy of an insider", who is "betraying his ancestral and anachronistic community into the modern anglicised world". That is fair comment, in terms of the play.
Yet the great body of material relating to the Ordnance Survey, in the custody of the Royal Irish Academy, allows of a parallel more nuanced interpretation.
Historical processes are often Janus-headed. In this instance, what had been conceived of as a scientific imperial project also became the instrument of recording and reclaiming a mainly Irish-speaking world about to be changed forever by the Famine.
The proposed publication by the survey of county-based memoirs began with a volume on the history and antiquities of Templemore, Co Derry, which was in effect a pilot project.
The wider programme, for which much of the research was completed, was halted by Sir Robert Peel's government, for fear it might stimulate "ancient" animosities.
Thomas Davis was enthusiastic about its potential to raise national feeling. A balanced account is contained in Gillian Doherty, The Ordnance Survey, History, Culture and Memory (Four Courts Press, 2004).
Three of the collaborators each became famous in their own right: George Petrie, landscape painter and historian, an early expert on the hill of Tara; Eugene O'Curry, who edited and translated Irish texts; and John O'Donovan, who edited the Annals of the Four Masters and published an Irish grammar.
Overseeing their work was a liberal English officer, Capt Thomas Larcom, who developed a great commitment to Ireland, and who carefully preserved the Ordnance Survey letters sent to him containing a wealth of information on every county.
They suggested to him the need for a National Museum, later founded in 1877. These letters were first published by Fr Michael O'Flanagan, vice-chairman of Sinn Féin from 1917, with new illustrated editions relating to seven counties recently republished by Four Masters Press. Larcom also oversaw the first full census of population in 1841.
The letters show that John O'Donovan had fierce national pride, which he did not conceal from Larcom.
He wrote from Trim on August 8th, 1836: "But why should not the ancient Irish families leave their names upon the lands possessed by them as well as the Anglo-Normans of Meath left theirs upon?" He could be scathing of the "half-civilised" gentry and Protestant clergy.
In 1834 he said the Presbyterians of south Belfast were grossly ignorant of names and antiquities and "so virulently prejudiced against anything that had belonged to ancient Ireland or the Papists".
O'Donovan noted of an encounter with a Down rector named Dubordieu: "He despised me for being a Paddy and a Papist whilst I, with all the folly of Milesian pride, looked upon him as an insignificant little clergyman of vitiated habits - as a rank Orangeman and a Huguenot."
The Royal Irish Academy (www.ria.ie) acquired last year - with the assistance of grants from the Heritage Council, Kilkenny Civic Trust and the Paddy Healy Trust - from Tralee antiquarian booksellers Maurice and Jane O'Keeffe a valuable collection of 27 family letters written by John O'Donovan.
In these letters, O'Donovan researches his 17th-century family history, in particular a first recorded ancestor, who had to flee Munster for killing with his bare hands the eldest son of O'Sullivan Beare in a land dispute.
He is deeply interested in the fate and rightful ownership of family lands in Cork, and who was the chief of the clan or sept of the O'Donovans.
Another family member, Capt Teige Donovan, was killed in 1690, attempting to take the garrison of Castletown, then in the possession of Col Townsend. Through these letters, one can see, like so many others, he was deeply affected by the sense of ancestral pride and dispossession running through Irish history, that is also one of the abiding themes of Friel's plays.