Both Nora and Krogstad committed...
In A Doll’s House, the relationship between Mr. Krogstad and Mrs. Linde contrasts the marriage between Nora and Torvald Helmer. Krogstad and Linde’s union is based on honesty and forgiveness; on the other hand, the Helmers’ marriage is sustained by dishonesty and illusion.
Both Nora and Krogstad committed the same crime—forgery—for similar reasons but experienced very different consequences. When Torvald’s health is failing due to overwork, Nora forges her father’s signature in order to obtain funds for her husband’s convalescence abroad. Nora essentially saves Torvald’s life while hiding her crime. No one ever discovers her guilt, allowing Nora to preserve their marriage and her status as an innocent kept woman. Torvald continues to view her simply as a doll; she dresses up for him and plays his pretty housewife. She perpetuates the illusion of their marriage as pure (i.e., lacking any skeletons in the closet) and the illusion of their roles (Torvald as the adult and Nora as the child).
On the other hand, Krogstad’s reputation is marred when he is caught for committing forgery in order to support his family. Society considers him corrupt; people look upon him as “morally diseased.” Yet the crime is not hidden from Linde, who states, “I think the sick are those who most need taking care of.” In fact, despite discovering Krogstad’s crime—which he committed after she left him to marry a wealthy man in order to support her family—Linde still wishes to reunite with him.
LINDE: Is it too late now?
KROGSTAD: Christine, are you saying this deliberately? Yes, I am sure you are. I see it in your face. Have you really the courage, then—?
LINDE: I want to be a mother to someone, and your children need a mother. We two need each other. Nils, I have faith in your real character—I can dare anything together with you.
Linde forgives Krogstad for his crime. Torvald, on the other hand, cannot handle the truth and forgive Nora for her crime, even though she committed it in order to help him. Her confession shatters his illusion of her as his darling treasure; he berates her:
What a horrible awakening! All these eight years—she who was my joy and pride—a hypocrite, a liar—worse, worse—a criminal!
Also, Krogstad and Linde’s relationship is based on equality and partnership. Linde proposes to Krogstad:
Nils, how would it be if we two shipwrecked people could join forces? ... Two on the same piece of wreckage would stand a better chance than each on their own.
Linde will not give up her future position at the bank in order to save Krogstad’s job and pride; nonetheless, she will not hold her economic dominance over him but care for him and share her life with him.
I could not endure life without work. All my life, as long as I can remember, I have worked, and it has been my greatest and only pleasure. But now I am quite alone in the world—my life is so dreadfully empty and I feel so forsaken. There is not the least pleasure in working for one’s self. Nils, give me someone and something to work for.
In turn, Krogstad now feels loved, secure, and confident enough to declare, "Now I shall find a way to clear myself in the eyes of the world."
In contrast, the Helmers' marriage is based on inequality and a dynamic of dominance and submission. Torvald treats Nora as a possession he can control; Nora plays along until she realizes his lack of respect for her. At the end of the play, she declares,
I saw you were not the man I had thought you were. …
I was so absolutely certain, you would come forward and take everything upon yourself, and say: I am the guilty one.
She is aware that he does not truly love her as a wife or equal. Nora sees that he values himself over her and would not defend her if her crime were exposed ... a crime which she committed in order to save him. She tells him,
As soon as your fear was over—and it was not fear for what threatened me, but for what might happen to you—when the whole thing was past, as far as you were concerned it was exactly as if nothing at all had happened. Exactly as before, I was your little skylark, your doll, which you would in future treat with doubly gentle care, because it was so brittle and fragile. Torvald—it was then it dawned upon me that for eight years I had been living here with a strange man
Unlike Krogstad and Linde's relationship, the Helmers' marriage is doomed due to lack of transparency and respect between both parties.