"Then you are most infallibly deceived, sweetest Jean" cried Lord Sydney; "my friend Trelawney does not love my sister Honoria, take my word for it. I should very deeply regret it if he did."
[Chapter 34, The Mysterious Marriage, or the Will of my Father, by Catherine G. Ward, pub 1820]
Using Christian names as a form of address
"To me, the sound of Mr. Bertram is so cold and nothing-meaning, so entirely without warmth or character! It just stands for a gentleman, and that's all. But there is nobleness in the name of Edmund. It is a name of heroism and renown; of kings, princes, and knights; and seems to breathe the spirit of chivalry and warm affections."
[Chapter 22, Mansfield Park, by Jane Austen]
Calling people by their Christian names was far less common than it is today. The use of given names was limited to family members: some husbands and wives, children and grandchildren, brothers and sisters, nieces and nephews, and some cousins, if you knew them well.
In certain circumstances, close friends might be on first name terms. Lower servants were also known by their first names.
Relatives
In her letters, Jane Austen referred to all her brothers, her sisters, her nieces and nephews by their first names. Whenever Lord Byron wrote to his half-sister Augusta Byron, (later Augusta Leigh) he always began his letters with "my dearest Augusta."
In Pride and Prejudice, the only person who calls Mr. Bingley by his first name is his sister Caroline. Siblings Henry and Eleanor Tilney, in Northanger Abbey, frequently address each other by their Christian names, while referring occasionally to their elder brother as "Frederick", even in the presence of their houseguest Catherine Morland.
In Mansfield Park, Frances Price addressed her cousins by their first names because she had been living with the family since she was ten years old, and occupied a similar position to that of a sibling. However, in Persuasion, Anne Elliot calls her father's heir and distant cousin "Mr. Elliot", because she only meets him for the first time during the story and he isn't especially well known to her.
In Sense and Sensibility, Edward Ferrars is on first name terms with the Dashwood family because his sister is married to Mr John Dashwood, so he is the equal of a brother to the Dashwood sisters.
In Emma, George Knightley is Emma's brother-in-law, because his younger brother was married to Emma's older sister. Although Mr. Knightley was described as an "old and intimate friend of the family", a "frequent visitor", and calls her "Emma", she continues to address him as "Mr. Knightley" right through the story. The sixteen year age difference between Mr. Knightley and Emma could explain some of the formality that he speaks of later in the book, after they become engaged:
"'Mr. Knightley.'--You always called me, 'Mr. Knightley;' and, from habit, it has not so very formal a sound.--And yet it is formal. I want you to call me something else, but I do not know what."
"I remember once calling you 'George,' in one of my amiable fits, about ten years ago. I did it because I thought it would offend you; but, as you made no objection, I never did it again."
"And cannot you call me 'George' now?"
"Impossible!--I never can call you anything but 'Mr. Knightley.' I will not promise even to equal the elegant terseness of Mrs. Elton, by calling you Mr. K.--But I will promise," she added presently, laughing and blushing--"I will promise to call you once by your Christian name. I do not say when, but perhaps you may guess where;--in the building in which N. takes M. for better, for worse."
[Chapter 53, Emma by Jane Austen]
So here, Emma seems to be saying that she will only call him George on her wedding day, and she doesn't seem to think it's at all odd to continue calling him "Mr Knightley" once they are married.
Couples
Couples who were married, or engaged to be married might choose to call each other by their first names in private, while maintaining formality when in public. In Pride and Prejudice, Elizabeth Bennet had just accepted Mr. Darcy's proposal when he first addresses her using her Christian name: "Such I was, from eight to eight and twenty; and such I might still have been but for you, dearest, loveliest Elizabeth!"
Any man overheard addressing a woman by her christian name (without being related or otherwise connected to her) would give rise to speculation that they were engaged, or worse. This was the case when Willoughby used Marianne's first name:
"His concern, however, was very apparent; and after expressing it with earnestness, he added, in the same low voice, "But, Marianne, the horse is still yours, though you cannot use it now. I shall keep it only till you can claim it. When you leave Barton to form your own establishment in a more lasting home, Queen Mab shall receive you."
This was all overheard by Miss Dashwood; and in the whole of the sentence, in his manner of pronouncing it, and in his addressing her sister by her Christian name alone, she instantly saw an intimacy so decided, a meaning so direct, as marked a perfect agreement between them. From that moment she doubted not of their being engaged to each other."
[Chapter 12, Sense and Sensibility, by Jane Austen]
A gentleman might also be on intimate, first name terms with his mistress or lover, although, depending on their relationship and his marital status they would be more circumspect when they meet out in public. However, while he would call her by her Christian name, she might still call him by his first name, surname, or his title alone if he had one.
"...call me your friend, your lover: call me Glenarvon—Clarence if you will. All these forms, these regulations, are odious amongst those who are attached. Say that you love, beloved Calantha: my own heart's friend, say it; for I see it and know it."
[Chapter 20, Glenarvon, vol 2, by Lady Caroline Lamb]
Glenarvon was written as a response to Lady Caroline's affair with Lord Byron; a relationship that he also referenced in writing:
"..."Promise not to love you!" ah, Caroline, it is past promising. But I shall attribute all concessions to the proper motive, and never cease to feel all that you have already witnessed, and more than can ever be known but to my own heart,—perhaps to yours. May God protect, forgive, and bless you. Ever, and even more than ever, Your most attached, Byron."
[Letter from Lord Byron to Lady Caroline Lamb, August 1812]
Female Friends
Two women who were very good friends might also call each other by their first names, after a decent amount of time. How quickly they moved from formality to the informality of first name terms would depend on the two people involved. Any difference in the status of the two ladies might delay or even discourage such familiarity.
When Emma Woodhouse first meets Harriet Smith, they limit themselves to the formality of "Miss Woodhouse" and "Miss Smith". As time passes, Emma begins to call her "Harriet Smith" and later addresses her by the more familiar "Harriet", but due to the difference in their social status, Harriet continues to call Emma "Miss Woodhouse" for the remainder of the story.
When Catherine Morland first meets Isabella Thorpe, they again begin with the formality of "Miss Moreland" and "Miss Thorpe", but being more equal in status than Emma and Harriet, the progress of their friendship had no limitations, and is only made easier thanks to the relationship that already existed between their brothers, James Moreland and John Thorpe.
"The progress of the friendship between Catherine and Isabella was quick as its beginning had been warm, and they passed so rapidly through every gradation of increasing tenderness that there was shortly no fresh proof of it to be given to their friends or themselves. They called each other by their Christian name, were always arm in arm when they walked, pinned up each other's train for the dance, and were not to be divided in the set."
[Chapter 5, Northanger Abbey by Jane Austen]
This contrasts with Catherine's relationship with Eleanor Tilney. Even though Catherine spends time with Eleanor in her own home as a guest, Austen doesn't explicitly show them using each other's Christian names until the moment Eleanor is forced to ask Catherine to leave.
Male Friends
Two men, who had known each other throughout their lives and were as close as brothers, might rarely call each other by their given names.
William Harness was described by Lord Byron as "the earliest and dearest I ever had from the third form at Harrow to this hour." Although he frequently addressed him in letters as "My dear Harness" he also, at least once, signed off at the end of his letters with "My dearest William, yours..."
"The calling of people by their Christian or surnames is a proof of affection as well as of hatred. They are generally the best good fellows with whom their friends take this sort of liberty. Diminutives are titles of endearment. Dr. Johnson's calling Goldsmith "Goldy" did equal honour to both. It shewed the regard he had for him. This familiarity may perhaps imply a certain want of formal respect; but formal respect is not necessary to if it is consistent with cordial affection."
[The Edinburgh Magazine and Literary Miscellany, Volume 82, pub. 1818]
In place of a christian name or surname, a Nickname or diminutive name might also have been used by very close friends, like that given to Sir Lumley Skeffington, known to his friends as "Skeffy".
Richard Brinsley Sheridan, the writer, was called "Sherry" by some of his friends, including Lord Byron.
John Jackson was a famous boxer of the time, known as "Gentleman" Jackson. He was another old friend of Lord Byron, who in his letters frequently addressed Jackson as "Jack", which could have either been a nickname taken from his surname or a diminutive of his Christian name:
"My Dear Jack, — You will get the greyhound from the owner at any price, and as many more of the same breed (male or female) as you can collect."
[Letter from Lord Byron to John Jackson, 12th December 1808]
Using Surname alone as a form of address
"My Dear Moore,—If you please, we will drop our former monosyllables, and adhere to the appellations sanctioned by our godfathers and godmothers."
[Letter from Lord Byron to Thomas Moore, 11th December 1811]
Throughout the 19th century, gentlemen regularly dropped the formality of "Mr" and addressed friends by their Surnames only. This was by far the most common way that men used to address other men of equal status with whom they were well acquainted.
The letter shown above was the first time Byron had addressed Thomas Moore by his surname. As previous letters written by him had begun with the more formal "Sir..." this might be considered, on Byron's part at least, to be extending the hand of friendship. Byron later described Moore as: ""a delightful companion, gay without being boisterous, witty without effort, comic without coarseness, and sentimental without being lachrymose."
Surnames were not only used between friends. Even among family members, gentlemen's surnames were frequently used as forms of address. Lady Catherine de Bourgh used both her nephews' surnames when calling to them during their stay in Kent:
"What is that you are saying, Fitzwilliam? What is it you are talking of? What are you telling Miss Bennet? Let me hear what it is."
"We are speaking of music, Madam," said he, when no longer able to avoid a reply.
"Of music! Then pray speak aloud. It is of all subjects my delight. I must have my share in the conversation, if you are speaking of music. ... How does Georgiana get on, Darcy?"
[Chapter 31, Pride and Prejudice, by Jane Austen]
And later, when Colonel Fitzwilliam was talking to Elizabeth, he used the same informality to refer to his cousin and Mr Bingley:
"I really believe Darcy does take care of him in those points where he most wants care. From something that he told me in our journey hither, I have reason to think Bingley very much indebted to him. But I ought to beg his pardon, for I have no right to suppose that Bingley was the person meant.''
[Chapter 33, Pride and Prejudice, by Jane Austen]
This practice of using surnames may have begun in school. In male boarding schools, like Eton or Harrow, boys were recorded in the registers by their surnames, unless they had a superior title, and it must have been natural for this habit to continue beyond their school years.
"Wheeler: This is very genteel of you, Talbot. I always thought you would do the genteel thing as I knew you to be so generous and considerate.
Talbot: Don't waste your fine speeches, Wheeler, I advise you, this election time. Keep them for Bursal or Lord John, or some of those who like them. They won't go down with me. Good morning to you. I give you notice, I'm going back to Eton as fast as I can gallop; and who knows what plain speaking may do with the Eton lads? I may be captain yet, Wheeler.
[Eton Montem, The Parent's Assistant, by Maria Edgeworth]
But even past their school or university years, men would usually address those they considered friends by their surname, and refer to them by their surname alone when talking to a third party.
"Teddesley, November 30th. I went to Tixall on Tuesday, the 10th of November. There were Luttrell, Nugent, Montagu, Granville Somerset (who went away the next day), and afterwards Granville Vernon, Wilmot, and Mr Donald. I never remember so agreeable a party."
[Diary entry from 1818, The Greville Memoirs, pub 1875]
When a man became engaged or married, his new wife's family might drop the formality of "Mr" and refer to or address their new son-in-law or brother-in-law by his surname only. In Pride and Prejudice Mr. Bingley was spoken of and addressed as "Mr. Bingley" right up until he became engaged to Jane, at which point Jane began to speak of him as "Bingley".
"Nothing could give either Bingley or myself more delight. But we considered it, we talked of it as impossible."
[Chapter 59, Pride and Prejudice, by Jane Austen]
Yet, earlier in the book, Elizabeth felt no sisterly affection for her new brother-in-law when Lydia returned from London: "Come, Mr. Wickham, we are brother and sister, you know. Do not let us quarrel about the past. In future, I hope we shall be always of one mind."
Using a gentleman's surname on its own, when you weren't already acquainted with him, was considered a vulgar familiarity:
"Knightley!" continued Mrs. Elton; "Knightley himself!--Was not it lucky?--for, not being within when he called the other day, I had never seen him before; and of course, as so particular a friend of Mr. E.'s, I had a great curiosity. 'My friend Knightley' had been so often mentioned, that I was really impatient to see him; and I must do my caro sposo the justice to say that he need not be ashamed of his friend. Knightley is quite the gentleman. I like him very much. Decidedly, I think, a very gentleman-like man."
Happily, it was now time to be gone. They were off; and Emma could breathe. "Insufferable woman!" was her immediate exclamation. "Worse than I had supposed. Absolutely insufferable! Knightley!--I could not have believed it. Knightley!--never seen him in her life before, and call him Knightley!--and discover that he is a gentleman! A little upstart, vulgar being, with her Mr. E., and her caro sposo, and her resources, and all her airs of pert pretension and underbred finery."
[Chapter 32, Emma, by Jane Austen]
Using Titles as a form of address
"...her son was going on to repeat what Mordicai had said to him, but Lady Clonbrony interrupted-- "Oh, my dear Colambre! don't repeat that detestable man's impertinent speeches to me. If there is anything really about business, speak to your father. At any rate, don't tell us of it now, because I've a hundred things to do," said her ladyship, hurrying out of the room."
[Chapter 5, The Absentee, by Maria Edgeworth]
Where an heir to a peerage bore a courtesy title, like Lord Colambre in The Absentee, that Title would be used in place of a first name, by parents, siblings or cousins, or a surname by friends.
The Duchess of Devonshire's son William bore the courtesy title Marquess of Hartington from birth. As a child, his siblings would have never called him William. He would have been addressed by everyone in the family as Hartington. Being a long name, it's not surprising that his mother shortened this to the diminutive "Hart".
Among peers who have come into their titles, those titles were also used as other men used surnames. In this third-party report of a conversation, Lord Worcester is talking about his friend, the Duke of Leinster:
"If Leinster were not my friend, said Worcester to a gentleman, who afterwards repeated it to me, pointing to Leinster, and myself, as we stood in the round room, waiting for his grace's carriage—if that young man were not my friend, I would make him walk over my dead body, before he should take Harriette out of this house."
[Memoirs, vol 2, by Harriette Wilson]
There are fewer written examples of this kind of address, as private conversations between friends were rarely written down, but here is another, recorded by Harriette Wilson, which shows Thomas Sheridan, son of Richard Brinsley Sheridan, talking about the Marquess of Lorne and the Duke of Argyle:
"I am come from my friend, Lorne, said Tom Sheridan. I would not have intruded on you; but that poor fellow he is really annoyed, and he has commissioned me to acquaint you with the accident, which obliged him to break his appointment; because I can best vouch for the truth of it, having, upon my honor, heard the Prince of Wales invite Lord Lorne to Carlton House, with my own ears, at the very moment when he was about to meet you in Somers-town. ... I asked Argyle, Tom Sheridan proceeded, how he had addressed his last letters to you? To the post office in Somers-town, was his answer, and thence they were forwarded to Harriette."
[Memoirs, vol 1, by Harriette Wilson]
[Image: An illustration by Hugh Tomson, from Emma, pub. 1896, illustrating chapter 7: "At this moment, perhaps, Mr. Elton is showing your picture to his mother and sisters, telling how much more beautiful is the original, and after being asked for it five or six times, allowing them to hear your name, your own dear name."]