Do you think Mme. Forestier should return the difference in value between the original necklace and the one she received as a replacement?

This is an excellent question. It is one which has probably occurred to many readers of "The Necklace" over the years. The fact that we wonder about this question shows the power of Guy de Maupassant's writing. We actually believe these people were real and that Mathilde Loisel actually lost that borrowed necklace one cold night in Paris. There can be no doubt that Madame Forestier has a moral obligation to compensate the Loisels for the difference between the value of the borrowed necklace and that of the imitation. She could do it either by paying them approximately 35,500 francs in cash or by giving them the necklace for 500 francs. The Loisels paid 36,000 francs for the replacement (although with all the interest on the borrowed money, it must have cost them twice that much).

It is impossible, of course, to look back into the past and see what really happened. Even if we could see into the past, we couldn't tell because the characters were fictitious. The best clue we have is in Madame Forestier's reaction to Mathilde's worn appearance and to her revelation of how she and her husband replaced the lost necklace with an imitation.

"I brought you back another exactly like it. And it has taken us ten years to pay for it. You can understand that it was not easy for us, for us who had nothing. At last it is ended, and I am very glad."

"Oh, my poor Mathilde! Why, my necklace was paste! It was worth at most only five hundred francs!"

Since Madame Forestier freely admits that her necklace was made of fake jewels, something she could have kept to herself, it would appear that she has no intention of profiting by her friend's mistake. Madame Forestier might find it hard to get her hands on 35,500 francs, so it seems likely that she would simply make Mathilde a gift of the necklace, which, after all, really belongs to the Loisels and not to her. Mathilde and her husband could at least receive some compensation for their ten years of toil and privation. They could sell the necklace for around 36,000 francs, which would provide them a little comfort and security in their old age.

In Maupassant's short story "The False Gems," also titled "The Jewels" in some translations, we are given a good idea of the purchasing power of 36,000 francs at that time. "Monsieur Lantin, then chief clerk in the Department of the Interior, enjoyed a snug little salary of three thousand five hundred francs...." Since the protagonist of that story is a chief clerk, he is probably earning more than Monsieur Loisel.

The ending of the story raises other questions. What would a rich woman like Madame Forestier be doing with an imitation diamond necklace? Why didn't she tell Mathilde it was a fake when she let her borrow it? How would Mathilde feel now that she realizes she was wearing a paste necklace during her moment of triumph at the Minister of Public Instruction's ball when she thought she was wearing diamonds? How would her husband react when she told him? Would he be angry? Or would he be glad to get the money?

It seems to me that Madame Forestier is not only morally but legally obligated to return the diamond necklace now that she has revealed the truth. The necklace does not really belong to her. At most she could only claim 500 francs for the one that was lost. Maupassant undoubtedly did not want to deal with this issue at the end of his story because it would spoil the shocking effect.