Authentic – adjective genuine, authoritative, true; (of writing) trustworthy, as setting forth real facts.
Verisimilitude – noun the quality of seeming real or true; an appearance of truth or reality.
Given the dictionary definitions above, writers of fiction must have both authenticity and verisimilitude. This has a specific relevance to writers of historical fiction.
To take my own novel, Reconquista, as an example, it is authentic in that it shows the city of Jerez besieged in 1264 by King Alfonso X. He was there and he did besiege the city ( even if historians debate the actual date upon which the city fell – see The wrong saint? ). It is inauthentic in that it also describes fictional events, like a cannon shot being the way that the siege ends, or a sea-battle off Tarif-al-Ghar in 1265 ( as far as I am aware, no such battle took place in that place at that time, although one did take place 600 years later ).
But often the line between authenticity and verisimilitude is blurred. Especially when it comes to characters in historical fiction who really existed. Most of the characters in Reconquista are products of the imagination, excepting the great and the good. So, King and Emir were real people, placed in real locations, though fictional thoughts and actions are given to them.
The Governor of Cadiz was a real person, though I don’t know whether or not he would really have done the things which the novel has him do, but as long as his character is consistent that’s okay. Readers of historical fiction aren’t, in the main, troubled by this. As long as one doesn’t have people, fictional or real, appearing in the past who couldn’t have been there, readers are generally content. So no Jack the Ripper or Neil Armstrong in thirteenth century Jerez, (though this happens in science fiction and fantasy of course).
By the same token, the writer of historical fiction can’t just transplant modern technology or modern mores into the past. No pistols or rifles in Reconquista then and no ‘liberated’ females, self-determining girls or women, independent and free in the sense that women are independent and free in 2017 Britain. Rebecca has her adventures in male disguise.
Sometimes, however, that which is authentic doesn’t seem true. When researching for the aforementioned sea-battle I found out quite a lot about the ships and naval weaponry of the time. I was surprised to discover that the Moors had developed a naval weapon, a canister containing explosive which was propelled through the water, a sort of prototype torpedo. Something interesting to include I thought.
That I didn’t was because I realised that readers wouldn’t credit it. The same happened with the name of a minor character, Atta’s neighbour. I originally called him Idris, an authentic Arab name, but everyone (including my editor) who read drafts of the book asked me why I’d placed a Welshman in 1264 Jerez. In vain I explained. The damage was done, the spell had been broken. Readers weren’t thinking about what Atta would find when he returned to his half destroyed home, but why his neighbour had a welsh name. The same would have happened with the sea weapon. So verisimilitude beats authenticity, in these instances at least.