ENGSTRAND. What the devil do you mean? Do you set yourself up against your father, you hussy? (1.34)
Engstrand knows he's not Regina's father, and there seems to be some evidence that she knows it, too. The idea of family is one of the social conventions Engstrand manipulates to his own advantage. He does the same thing with religion.
MANDERS. But a daughter's duty, my good girl – Of course, we should first have to get your mistress's consent. (1.127)
Engstrand has set Manders on the case of getting Regina back to town. Manders is happy to oblige.
MRS. ALVING. Ah, but here he has his mother, you see. My own darling boy – he hasn't forgotten his old mother! MANDERS. It would be grievous indeed, if absence and absorption in art and that sort of thing were to blunt his natural feelings. (1.154-155)
This assumption of filial loyalty is one of the "ghosts" Mrs. Alving clings to until the very end of the play.
MANDERS. That is a very disputable point, Mrs. Alving. A child's proper place is, and must be, the home of his fathers. (1.307)
Pastor Manders is rigid and conventional in his thinking. He can't admit there might be some factors that would move a child's proper place from the home of this father. He fights for this with Regina, too.
MANDERS. But I'm not talking of bachelors' quarters. By a "home" I understand the home of a family, where a man lives with his wife and children. OSWALD. Yes; or with his children and his children's mother. MANDERS. [Starts; clasps his hands.] But, good heavens! (1.319-321)
Cohabitation is so common now in some communities that it might be hard for some readers to understand the Pastor's shock. Try substituting something a little less established when you imagine the Pastor's resistance.
MANDERS. You found it troublesome to be a mother, and you sent your child forth among strangers. (1.370)
Sitting in the audience, we can't yet know the irony of this statement. We discover later that Mrs. Alving would have loved to keep her son, and only suffered his absence to save him.
MANDERS. You call it "cowardice" to do your plain duty? Have you forgotten that a son ought to love and honour his father and mother? MRS. ALVING. Do not let us talk in such general terms. Let us ask: Ought Oswald to love and honour Chamberlain Alving? (2.55-56)
This exchange typifies Manders and Mrs. Alving's different approaches to the world. Pastor Manders accepts a rule and sticks to it. Mrs. Alving worms around inside the rule to investigate it more closely. Which approach is a better recipe for happiness?
MRS. ALVING. Do you really mean "unheard of"? Frankly, Pastor Manders, do you suppose that throughout the country there are not plenty of married couples as closely akin as they? (2.74)
Mrs. Alving's suggestion that Oswald and Regina live openly together is surprising. The idea of incest doesn't bother her – it's the idea of deceit she can't stand.
MRS. ALVING. You know I would ten times rather forgo the joy of having you here, than let you – (2.225)
Mrs. Alving is proposing the same old self-sacrifice that has made her life so miserable. Putting her son before her is her old ghost of habit. It's also the reason Oswald gravitates towards Regina.
OSWALD. He said, "The sins of the fathers are visited upon the children." (2.270)
This is a very classical idea explored in the Bible, Euripides, and Shakespeare. The notion of a guilt passing through generations helps give the play its epic scope.
MRS. ALVING. This is terrible to think of! Ought not a son to love his father, whatever happens? OSWALD. When a son has nothing to thank his father for? has never known him? Do you really cling to that old superstition? – you who are so enlightened in other ways? (3.168-169)
It's interesting that, even in the third act, Mrs. Alving repeats such a Manders-like idea. She may have argued with the Pastor about it, but she still believes in familial love as a deep obligation.