MANDERS. [Lowering his voice.] But one should not talk about it, Mrs. Alving. One is certainly not bound to account to everybody for what one reads and thinks within one's own four walls. (1.181)
Depending on how it's played, this can be a laugh line. Pastor Manders's point is you may think whatever you want, but keep it to yourself. Publicly announcing your eccentricities can only disturb others and upset the status quo.
OSWALD. Well, then, allow me to inform you. I have met with it when one or other of our pattern husbands and fathers has come to Paris to have a look round on his own account, and has done the artists the honour of visiting their humble haunts. They knew what was what. These gentlemen could tell us all about places and things we had never dreamt of. (1.337)
Hypocrisy is a special breed of "lies and deceit" within the play. Oswald becomes distraught recounting the hypocrisy of so-called "pattern husbands" – but in truth, almost everyone in the play is guilty of hypocrisy in some form or another.
MANDERS. It almost makes me dizzy. Your whole married life, the seeming union of all these years, was nothing more than a hidden abyss! (1.396)
Manders agrees that Mrs. Alving could do nothing but hide the truth. As someone who cares for her, however, he rues that things turned out that way.
MRS. ALVING. That has been my ceaseless struggle, day after day. After Oswald's birth, I thought Alving seemed to be a little better. But it did not last long. And then I had to struggle twice as hard, fighting as though for life or death, so that nobody should know what sort of man my child's father was. (1.399)
Mrs. Alving wrote lying letters to her son, describing his father as a hero. She worked hard on the estate and gave Captain Alving all the credit. She took care of the Captain's illegitimate child. It must have been exhausting to keep up such a juggernaut of lies.
MRS. ALVING. [Drumming on the window frame.] I ought never to have concealed the facts of Alving's life. But at that time I dared not do anything else-I was afraid, partly on my own account. I was such a coward. (2.46)
Mrs. Alving takes the blame for deceiving her son. In calling herself a coward, she seems to admit that her motives for protecting Alving's reputation weren't completely pure and self-sacrificing.
MRS. ALVING. [Looking steadily at him.] If I were what I ought to be, I should go to Oswald and say, "Listen, my boy: your father led a vicious life – " (2.50)
Compare this fantasy of hers – coming clean about her husband's vicious life – with her understanding of Captain Alving at the end of the play. It seems as though she learns empathy.
MANDERS. And this is how you reward me! You cause me to enter falsehoods in the Church Register, and you withhold from me, year after year, the explanations you owed alike to me and to the truth. Your conduct has been wholly inexcusable, Engstrand; and from this time forward I have done with you! (2.146)
Just a moment ago the Pastor was reassuring Mrs. Alving that lying was appropriate, now he seems to be defender of the truth. It looks like he may have had his ego bruised.
ENGSTRAND. Oh, that'll be the way of it, all the same. I know a man as has taken others' sins upon himself before now, I do. (3.71)
Pastor Manders accepts Engstrand's offer to cover up the Pastor's involvement in the fire – though it's by no means certain that it was his fault. The Pastor and Engstrand embark on more lies, just as Mrs. Alving and Oswald are about to confront a terrible truth.