The Major was venomously opposed to the awful fast-food places that were gradually taking over the ugly stretch of road between the hospital and the seafront, but he was prepared to find her indulgence charmingly out of character. (2.27)
The Major loves his village and his charming English countryside because of the sheer character of the place. He sees the chain restaurants as out of character because they stand out so much: they're loud and garish, the opposite of country charm.
"I did give him up for many decades," she said. "He seemed such a part of those who refuse to reconsider what the Empire meant. But as I get older, I find myself insisting on my right to be philosophically sloppy. It's so hard to maintain that rigor of youth, isn't it?" (5.45)
Mrs. Ali seems to have relaxed some of her principles as she's grown older. This becomes a recurring theme, as the Major learns to do that as well. In fact, they both try to help and the much younger Abdul Wahid relax his principles, too. People of any age can be inflexible, and people of any age can change.
"I rather admire such refusal to bow before authority, but I fear it makes for a very uncomfortable daily existence." (5.96)
Here is the Major trying to tell Abdul Wahid to loosen up. In the long run, putting principles ahead of people just isn't worth it—at least that's not what the Major has learned over the years.
"What I meant to say, Mrs. Green, is that while last year's them was most creative […] not all the guests carried on in the decorous manner that I'm sure you had counted upon." (6.48. 6.50)
This is a biting insult from the Major to the party-planning committee. Do they really "count upon" the dance being "decorous"? It seems they're actually planning parties that make people go wild, just so they can have something to gossip about. It's like high school never ends.
He was very touched by his lordship's words and by the always respectful use of the Major's rank. His lordship could so easily have called him Pettigrew, and yet he never did. In return, the Major never referred to him in the familiar, even behind his back. (6.98)
Principles aren't just for the working class, like Abdul Wahid, or the middle class, like the Major. Lord Dagenham is also respectful—but only when it comes to English tradition and matters of title. He has no principles when it comes to selling his land to an American developer.
"I have already asked Mrs. Ali to attend as my guest," [the Major] said. (11.151)
The Major is a consummate gentleman. He invites Mrs. Ali to the dance, both to protect her from further discrimination and because he really wants to.
"At least Abdul Wahid showed up when invited." (13.17)
Roger has tons of insulting things to say about Abdul Wahid, but the Major is quick to remind Roger that Abdul Wahid has more manners in his little finger than Roger does in his whole body.
"With your military background, you understand better than most men the concept of honor and pride." (14.52)
Are the Major's principles built on his military background? If he hadn't been in the military, would he act just as gentlemanly as he does?
The Major felt despair strike him like a blow to the ar. He had defended the wrong woman. (17.175)
The biggest internal conflict the Major must face is the one in which he realizes that he isn't a principled as he believes himself to be. Or, his principles aren't in line with how he now wants to behave. He defends Grace at a party out of instinct, to defend a woman and to defend someone in his own social class. By doing this, he neglects to defend Mrs. Ali when she really needs the ally.
"I do not blame you for the rudeness of others," [Mrs. Ali] said. (21.66)
Mrs. Ali isn't as juvenile as many of the village ladies are. She understands that the Major's actions reflect on himself and himself alone.
"Either shoot me or chose to live yourself," said the Major. "I can't face your aunt any other way. How strange to think that we come as a pair now." (24.124)
The Major knows that the best way to impress Mrs. Ali is by being a gentleman, and he's going to talk Abdul Wahid down from his rocky ledge even if it kills him. The Major was initially driven by his belief that the pair of guns should be reunited, but by the end of the book, he's found a different pair—himself and Mrs. Ali.