Oswald has a lot in common with Henrik Ibsen, the author of Ghosts. Oswald is from Norway but lives in the South (Paris). Ibsen lived in Rome for most of his life, though he continued to write about his homeland. He loathed what he considered the small-minded and puritanical outlook of his countrymen – and they loathed him back, especially when it came to Ghosts. (See "In a Nutshell" for more on this.) Ibsen himself was an iconoclast, meaning he freely expressed his rejection of accepted ideas and institutions. His spokesperson here is Oswald, a non-conformist and an artist struggling to defend his identity in the hostile, judgmental environment of his home.
Oswald is a straight shooter. While Pastor Manders and Mrs. Alving often beat politely around the bush, Oswald says what he means. In his first appearance, he chats with Manders for only a couple minutes before he's speaking his mind in defense of unconventional romantic relationships. He gets worked up as he recalls the hypocrite husbands who treat artists' quarters like they are brothels. Then he remembers where he is and apologizes: "Excuse me, Pastor: I know you can't take my point of view; but I couldn't help speaking out" (1.344).
Oswald is also merciless with his mother. He rejects her maternal sentimentality. In Act 3, he's just told her that a) he doesn't love his father, and b) he doesn't love her. Oswald doesn't accept the idea that just because he came from Mrs. Alving's womb he owes her something. There's that rejecting-accepted-ideas thing again. He asks why should love her? He didn't grow up living with his parents, he doesn't know them, and coming home is just depressing. He'd rather be in Paris. When Mrs. Alving redoubles her efforts to win his heart, he asks her to stop talking about it, since he has other things on his mind:
MRS. ALVING. Oh, I could almost bless the illness that has driven you home to me. For I see very plainly that you are not mine: I have to win you.
OSWALD. [Impatiently.] Yes yes yes; all these are just so many phrases. You must remember that I am a sick man, mother. I can't be much taken up with other people; I have enough to do thinking about myself. (3.178-179)
Oswald's painfully honest communication style is appropriate to his function in the play. His return home forces Mrs. Alving to confront the truth of her life. She wants to bury her past – and by her past we mean the memory of her alcoholic, philandering husband – but she just can't. The past lives in the present. If she didn't have her rose-colored maternal glasses on, she would recognize that fact when Oswald comes down smoking the pipe in Act 1. He's Captain Alving all over again, as Manders recognizes: "there is an expression about the corners of the mouth – something about the lips – that reminds one exactly of Alving: at any rate, now that he is smoking" (1.282).
If Pastor Manders is the representative of law, order, and society, Oswald is the representative of unruly life and passion. Joie de Vivre. The Joy of Life, or Livsglede in Dano-Norwegian. Personal freedom. Choosing your destiny. He articulates his position in Act 2, as Mrs. Alving raptly listens:
OSWALD. I only mean that here people are brought up to believe that work is a curse and a punishment for sin, and that life is something miserable, something; it would be best to have done with, the sooner the better….But in the great world people won't hear of such things. There, nobody really believes such doctrines any longer. There, you feel it a positive bliss and ecstasy merely to draw the breath of life. Mother, have you noticed that everything I have painted has turned upon the joy of life? – always, always upon the joy of life? – light and sunshine and glorious air-and faces radiant with happiness. That is why I'm afraid of remaining at home with you. (2.379-380)
When Oswald paints a picture of this free, happy life, Mrs. Alving suddenly understands what her husband lacked, why he went so far downhill in the gloomy, duty-bound life of the North. He was suffocated and paralyzed – and under her control.
No one ever says the word "syphilis" in this play, but that's what Oswald's got. It's a sexually transmitted disease that can also pass from a mother to a baby. It doesn't make sound medical sense that Oswald got it from his father – but Ibsen is most interested in the metaphor: "The sins of the fathers are visited upon the children" (2.270).
The kind of syphilis Oswald seems to have is "tertiary" or "latent" syphilis. It's been dormant in his body and is just emerging, causing the headaches and fatigue he complains about. Untreated (or treated too late), it can result in serious organ and nerve damage, paralysis, muscle deterioration, blindness, and dementia. Oswald is more colorful in his description of the illness; his doctor calls it "a sort of softening of the brain – or something like that. [Smiles sadly.] I think that expression sounds so nice. It always sets me thinking of cherry-coloured velvet – something soft and delicate to stroke" (3.219).
Oswald's decline means that Mrs. Alving has to let go of the final "ghost" in her life – her attachment to her son.