What is Bartleby's disorder? Antisocial personality disorder, avoidant personality disorder, post traumatic stress disorder, borderline personality disorder, major depression, paranoid personality disorder, acute stress disorder, or schizophrenia?
Yours is an intriguing question. However, I don't see how anyone can hope to make an accurate diagnosis of a fictional character. Bartleby is just a creation of Herman Melville. If Bartleby seems like a real person this is because of the talent of the author. Fiction writers have a standard way of creating believable characters. This is to give them one dominant trait and one contrasting or complementary characteristic. This will tend to create an illusion of a human being, but not a real human being. Some authors, of course, are better at it than others. Bartleby is an extreme introvert. C. G. Jung coined the terms "introvert" and "extravert" in his book Psychological Types. But he certainly did not invent the types. People, including fiction writers and dramatists, have recognized these types for centuries. Hamlet, for example, is obviously an introvert. Herman Melville has his story narrated by a man who is obviously an extreme extrovert. This is for the sake of contrast. How can an extreme extrovert understand an extreme introvert? Extroverts tend to pressure introverts to act more like extroverts; whereas introverts do not try to pressure extroverts to act like introverts. Although Bartleby seems cold and standoffish, there is something likeable about the man. This would be his contrasting trait, creating the combination of traits that make a character seem human. That contrasting trait may be self-assurance. He is an introvert who has the courage to be himself. He doesn't try to act like an extrovert. He is a very quiet sort of rebel. He is in exactly the right profession. C. G. Jung says specifically that trying to act like something we are not leads to neurosis and that the cure for neurosis is for the neurotic to understand who he is and to be himself. Herman Melville was not a psychologist but a fiction writer. He wasn't trying to portray any of the disorders you name in your question. Most of them were unknown and unclassified in Melville's time. But everybody knew there were introverts and extroverts, regardless of the fact that they didn't have those words to describe them. I think we can go way too far in trying to analyze characters who are, after all, nothing but names on paper, nothing but illusions--and our own illusions at that. So many people try to do that with Holden Caulfield!
C. G. Jung in his book Psychological Types coined the terms "introvert" and "extravert," (now more commonly spelled "extrovert") which rapidly came into popular usage because, as he said, such types are so obvious and have always been so generally known. With Bartleby, Melville seems to be presenting a portrait of an extreme introvert, almost a caricature of the type. There is nothing particularly wrong with Bartleby. He just has a hard time surviving in a world which is dominated by extraverts, in which employers are looking for "team players" and generally outgoing types. According to Jung's great book, many introverts have to pretend to be extraverts in order to survive and to be socially accepted. Bartleby is an introvert who accepts himself and refuses to be a team player. Jung states that people who spend their lives trying to be something other than what they really are will develop neuroses and can only be cured by learning to accept themselves.
Extraversion is "the style of the times" in the western world, and nowhere more so than in the U.S. Bartleby might not be considered weird if he lived in a country like India, but he is in New York City, which might be the extraversion capital of America, and he works in Wall Street, which might be the epicenter or nucleus of that extraversion capital.
Here is a significant quote from Jung's book, with the part about modern art championing subjectivity (which is virtually synonymous with introversion) set off in boldface:
The introvert is far more subject to misunderstanding than the extravert, not so much because the extravert is a more merciless or critical adversary than he himself might be, but because the style of the times which he himself imitates works against him. He finds himself in the minority, not in numerical relation to the extravert, but in relation to the general Western view of the world as judged by his feeling. In so far as he is a convinced participator in the general style, he undermines his own foundations; for the general style, acknowledging as it does only the visible and tangible values, is opposed to his specific principle. Because of its invisibility, he is obliged to depreciate the subjective factor, and must force himself to join in the extraverted overvaluation of the object. He himself sets the subjective factor at too low a value, and his feelings of inferiority are his chastisement for this sin. Little wonder, therefore, that it is precisely in the present epoch, and particularly in those movements which are somewhat ahead of the time, that the subjective factor reveals itself in exaggerated, tasteless forms of expression bordering on caricature. I refer to the art of the present day.
"Bartleby the Scrivener" might be considered art that is ahead of its time. Maybe the disorder is not Bartleby's but the disorder of society.
The Myers-Briggs type indicator test has become widely used in business, academia, and elsewhere. It is firmly based on Jung's Psychological Types. Versions of this test may be accessed online via Google and taken without charge. The results will show which of sixteen psychological types the test-taker belongs to and suggest which career choices might be best for that individual.
The Romans believed in the four temperaments: choleric, sanguine, melancholic, and phlegmatic. Using these as measurements of Bartleby, he is phlegmatic. The character represents the passive side of man, that which "prefers not to" do anything but be the recipient of what others will provide. He lacks all ambition. Perhaps this aligns with avoidance personality disorder.
I don't have anything but a layman's understanding of these terms, but it seems to me Bartleby is suffering from a lack of inspiration and satisfaction in his life which cause him to respond in his passive-aggressive manner. "I would prefer not to" implies he could, and he would, but something is keeping him from actually doing it. Being reduced to this miserable and unfulfilling job (and, apparently, his life) has caused this reaction, and I'm not sure it's due to any of the "disorders" you've given.
I am not a therapist, but by a process of elimination, my guess would be major depression. There is nothing to suggest that Bartleby is out of touch with reality. He is not hearing voices, for example, or seeing anything that is not there. He does not really act to avoid all human connection, just certain activities. Could working in a dead letter office create PTSD? I don't think so, although I must say that if one placed May from The Secret Life of Bees in such an office, she might have experienced this disorder. Borderline personality disorder usually involves more dramatic forms of manipulation. Bartleby is utterly passive, in a way that is often manifested in major depression, a kind of tyranny of weakness.
The key, I believe, is his overidentification with his previous employment in the "dead letter" office. It seems to me that he considers himself to be a kind of dead letter that has arrived at its destination, first the narrator's office, and ultimately, the Tombs. What better place for a dead letter than a "tomb"?
The other option that occurs to me is that Bartleby is suffers from an autism spectrum disorder. He functions far better with things than with people, and his sole "line" suggests that someone taught him one way to express his preferences, or lack thereof, with human beings, and he does not have the wherewithal to articulate other ideas.
I will be interested to know what other people think.
Bartleby the scriver is probably just as ambiguous when it first came out. Melville does not seem to provide enough information to understand the scrivener. From the first scene in the story, the lawyer apparently confesses his inability to understand Bartleby, when he says Bartleby is "one of those beings of whom nothing is ascertainable," and for whom "no materials exist, for a full and satisfactory biography".
This would lead the reader to believe that the lawyer is either witholding information or too professional as a lawyer in his description of Bartleby for readers to accurately gage the character. The lawyer, it seems, is an unreliable narrator.
Bartleby discovers the place to be "a solitary office, upstairs, of a building entirely unhallowed by humanising domestic associations" in a building "deficient in what the landscape painters call life."'
Bartleby seems to be a product of his environment, therefore I wouldn't say that has any disorder other than to appreciate his last place of employment. he might "function better with things than with people," but who doesn't working in an intolerable situation.