His only fault indeed seems modesty. if he were less modest, he would be more agreeable, speak louder & look impudenter; —and is not it a fine character, of which modesty is the only defect? —i have no doubt that he will get more lively & more like yourselves as he is more with you; —he will catch your ways if he belongs to you. in this passage from “on making an agreeable marriage,” what does jane austen say is the problem with mr. j. p., and what does she advise fanny to do to change mr. j. p.?

Jane Austen finds that the only defect in Mr. J. P. is his modesty.

She then advised Fanny to try to spend more time with the man and see that he might change, becoming more like her.

Explanation:

"On Making an Agreeable Marriage" is the title of the numerous letters that Jane Austen wrote to her niece Fanny regarding her feelings for the girl's future husband. She wrote the letter to show her confusion and yet inquired about the matter where Fanny seemed to be less in love with the man the more he loves her.

In the given passage, Jane mentions that the only problem that she finds in her niece's fiance is that he is too "modest". The only defect that she can find in the young man is his "modesty" which is not at all a bad thing. But considering the turnabout of Fanny's feelings for the man. It is as if "being secure of him had made you indifferent", implying that the more he seemed to love her, the more repulsed she was by his love.

She advised her to try to spend more time with him so that it might further lead to his change in his personality. She told her that he might "get more lively & more like yourselves as he is more with you;—he will catch your ways if he belongs to you". This shows she's in favor of the union and wished she (Fanny) would also see the good man he is, even with her conflicting feelings.  

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