In East of Eden, how is chapter 25 a turning point in the story and for Adam's character?
In Chapter Twenty Five, Adam sees Cathy for the first time in years. After Samuel Hamilton’s funeral, he proceeds to get a bit drunk and seek out Kate’s brothel.
Samuel described Kate and her depraved whorehouse as “medicine” to Adam, seeking to shock Adam into living once more. Adam reacted unfavorably, literally running away from the weight of the knowledge; his calm demeanor in the whorehouse belies the depth to which it shook him. Upon viewing Kate once more, Adam finds himself noting that he has never truly seen her before, blinded as he was by his own misconceptions. Throughout the conversation, Kate becomes more and more belligerent while Adam stays calm. Even the knowledge that Kate slept with Charles only prompts Adam to make an inner revelation that it didn’t matter. He would love his sons regardless. He leaves under threat, but is composed and recommitted to his family and life.
The scene is a major turning point for Adam, who is a largely passive character. He joined the army because his father expected it of him, wandered aimlessly for years after, and refused to name his sons for a year after Cathy left him: agency has never been his strong suit. And yet, guided by the idea that “thou mayest,” he takes control of his own life in this scene. He has started to become his own man, and the change is clear to those near him in the next chapter.
Adam's rejection of Cathy shows he is through with her: he will not be manipulated by her again. Now that he knows who she is, he is left with a different question: how will this affect his sons? The source of his conflict has changed.