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.

A Doll's House ends on a note of hopefulness, though the hope is rather a weak one and based far off in the future. As she leaves, Nora refers to "the most wonderful thing of all," which would have to happen for her to become Torvald's wife again. This marriage would be a partnership of equals, in which husband and wife could respect each other and be honest.

The type of marriage to which Nora refers, whether she makes the connection or not, is the union between Mr. Krogstad and Mrs. Linde. This is a relationship made possible by the many trials the two of them have endured and their acceptance of each other's flaws. Torvald arrogantly looks down on Krogstad as a man without honor, whose presence makes him physically sick. Mrs. Linde might also be regarded as having disgraced herself by marrying for money. However, both these flawed individuals had reasons for the way they behaved, and they have grown as a result of their compromises and suffering. Their marriage will be quite unlike the picture-perfect fantasy acted out by the Helmers in act 1 of the play.

Perhaps the first step of many that Torvald will have to take if he is to enter into a true marriage with Nora is to recognize that Krogstad is not merely a sickening villain but a man whose crooked path in life has something to teach Torvald himself. Krogstad's relationship with Mrs. Linde, unlike Torvald's own marriage to Nora, is based on self-knowledge, tolerance, understanding, and acceptance of imperfection. A comparison between the two relationships highlights the lack of all these qualities in the Helmers' sham marriage.

The relationship between Krogstad and Mrs. Linde acts as a foil to that between Nora and Torvald. This means that it brings out certain characteristics of the Helmers' marriage, most notably the lack of genuine love, mutual respect, and communication.

Torvald may think that he loves Nora, but his infantilization of her would seem to suggest otherwise. Also, the patronizing way that he addresses her—talking down to her as if she were a child rather than a grown woman—indicates a marked lack of respect. In addition, the huge power imbalance between husband and wife closes down the possibility of any meaningful communication between the two.

The contrast between the Helmers' relationship and that enjoyed by Krogstad and Mrs. Linde couldn't be greater. Despite the huge setback that their relationship received when Mrs. Linde married for money, they have managed to pick up where they left off, reestablishing a relationship that soon leads to marriage.

And unlike the Helmers' marriage, this is a marriage based on genuine love and mutual respect. What's more, it is a marriage of equals, in which two “shipwrecked souls,” in the words of Mrs. Linde, have joined hands together. There is no imbalance of power here; the same cannot be said of the Helmers' marriage.

Mrs. Linde and Mr. Krogstad were so in love at one time. However, Mrs. Linde was forced to marry another man because of her unfortunate circumstances. Having a sick mother and small brothers to care for, Mrs. Linde chose to marry a man who had financial stability. This broke Mr. Krogstad's heart.

As the story unfolds, Mrs. Linde, now a widow, comes back into town. She reunites with Krogstad. Krogstad and Mrs. Linde can communicate openly. This is a characteristic that is missing in the Helmer's relationship.

Mrs. Linde and Krogstad are completely honest with one another. This is a characteristic that is missing in the Helmer's marriage.

Mrs. Linde and Krogstad respect one another. This is a characteristic that is missing in the Helmer's relationship.

Torvald and Nora keep secrets. Well, at least Nora keeps secrets from Torvald. Torvald treats Nora as a child. He does not respect her intellect. On the contrary, Mrs. Linde and Krogstad see one another as equals. They are willing to stand side by side. Krogstad is not condescending as Torvald is to Nora.

Although Krogstad and Mrs. Linde have been through some difficult times, they are so fortunate to have found love one for the other once again. True love seems to be a missing element in the Helmer's relationship. No doubt, the Helmer's could take a lesson in love from Mr. Krogstad and Mrs. Linde:

At the end of the play, she and Krogstad are reconciled, but it is Mrs. Linde who decides that Nora and Torvald must face their problems. Thus, she stops Krogstad from retrieving his letter and moves the play toward its conclusion.

It is sad that the Helmer's do not have the genuine, loving relationship that Mr. Krogstad and Mrs. Linde have found in one another.