How is slim a foil for curley

Though the boss seems fair-minded, treating his men to whiskey at Christmas and giving Lennie and George the benefit of the doubt, he is an unimportant character. Instead, his son Curley embodies authority on the ranch. In the book’s vision of the world, Curley represents the vicious and belligerent way in which social power tends to manifest itself. Given Curley’s temperament, he serves as a natural foil—a character whose emotions or actions contrast with those of other characters—for both the gentle Lennie and the self-assured Slim. Whereas Curley is plagued by self-doubts that cause him to explode violently, Slim possesses a quiet competence that earns him the respect of everyone on the ranch. Like Curley, Slim stands as an authority figure. The men on the ranch look to him for advice, and, later, even Curley will deliver an uncharacteristic apology after wrongly accusing Slim of fooling around with his wife. Slim’s authority comes from his self-possession; he needs neither the approval nor the failure of others to confirm his stature. Curley’s strength, on the other hand, depends upon his ability to dominate and defeat those weaker than him.

The details that best show evidence of tribal traditions are, "never in the history of his people had a man married a woman who spoke a different tongue” and "it has never been heard," was the verdict of an old man speaking a few weeks later.