There are two kinds of conflict in de Maupassant's "The Necklace," though one is certainly more dominant. External conflict includes man vs. man, man vs. society, and man vs. nature. In this story, there are only a few examples of external conflict. Madame Loisel is poor in a world where other people are rich; once they incur the debt, she is forced to work in jobs which are looked down upon by society; someone kept the necklace she lost. These are all kinds of external conflicts.
The primary source of conflict in this story, though, is Madame Loisel's discontent with her lot in llife. her husband thinks her cooking is delicious; she is ashamed of how ordinary her cooking is because she can afford no better. Her husband thinks getting to go to a party is a good thing; she thinks it's only another opportunity to show the world all she does not have. Her husband thinks she looks beautiful with simple flowers for adornment; she is content with nothing less than sparkling jewels. She is too proud to admit the truth about the necklace--a choice that costs both of them everything, yet it clearly also made her a better person. It is her own inner struggles with pride that provide most of the conflict in this story.
Having served as a civil servant himself, Guy de Maupassant often satirized the class to which these civil servants belonged. Often his works contain subtle social commentary. Such a story is "The Necklace" in which Mathilde Loisel is
one of those pretty and charming girls, born, as if by an accident of fate, into a family of clerk. With no dowry, no prospects, no way of any kind of being met, understood, loved, and married by a man both prosperous and famous, se was finally married to a minor clerk in the Ministry of Education.
In this first paragraph, Maupassant already sets Mme. Loisel in conflict with society. For she could easily have been a lady had her parents been wealthy. Consequently, she is as "unhappy as a woman who has come down in the world" because she possesses
natural poise,...instinctive good taste, and ..[the] mental cleverness [that] make daughters of the common people the equals of ladies in high society.
Thus, because Mathilde Loisel realizes that she could be the equal of aristocratic ladies, she is discontent and places excessive value upon material possessions as she perceives monetary things being the means to higher positions in society. This is why she thinks that Mme. Forestier has loaned her a real diamond necklace, for in her mind, no wealthy woman would possess faux diamonds; this is why she does not confess to Mme. Forestier that she has lost the necklace. She is too proud to admit such a fault, already feeling inferior.
Throughout the narrative of Maupassant's story, Mme. Loisel sees herself as the "accident of fate" as Maupassant writes in the first paragraph. She is meant to be a lady, but is denied this role because she is the child of a civil servant and has married a civil servant. Her obsession with this idea prevents her from appreciating what a kind, generous person her husband is, and what a kind friend Mme Forestier has been. Thus, Mme. Loisel's conflict with her social position becomes internalized and is, then, an internal conflict of person versus self. Indeed, it is her pride that causes her to live the miserable years in payment for the diamond necklace.
I think that it is just man vs. self because she is not happy where she is in society.