After Darnay's trial for treason and his last minute release from the throws of death, Sydney Carton tells Charles Darnay,
"This is a strange chance that throws you and me together. This must be a strange night to you, standing alone here with your counterpart on these street-stones?"
Evidently, Darnay has not noticed more than the physical resemblance between them, for he replies,
"I hardly seem yet...to belong to this world again."
Carton then offers to take Darnay to dinner, entwining his arm in a physical act that indicates the mirroring of the two men. Dickens writes that Darnay is confused by the emotion of the day, feeling "his being there with this Double of coarse deportment to be like a dream," so he does not answer Carton questions, being at a loss for words. However, as Carton continues, he mentions Miss Manette and Darnay remembers that the rather coarse barrister has been responsible for saving his life; consequently, he expresses his gratitude. "I neither want any thanks, nor merit any," Carton carelessly replies, noting that he does not even know why he acted as he has. Then, in a spontaneous moment, he asks Darnay, "Do you think I particularly like you?"
In response to this question, Darnay answers candidly that Carton has acted in a caring way towards him, but Darnay does not think that the lawyer really does like him. Carton agrees: "I don't think I do....I begin to have a very good opinion of your understanding."
While Darnay's response may not be exactly courteous, it is honest and frank, and candor is what Carton respects in this situation; besides, the question is not exactly polite itself. But, clearly, Carton sees reflected in his doppleganger the man that he could have been had he not lived a dissipated life.