Tom begins the novel in possession of a practical sort of self-interest. Four years in prison, he claims, have molded him into someone who devotes his time and energies to the present moment. The future, which seems illusory and out of reach, does not concern him. He adopts this philosophy toward living not because he is selfish but as a means of coping: he fears that by putting his life in a context larger than the present day, he will drive himself mad with anger and helplessness. Of course, Tom, who exhibits a rare strength, thoughtfulness, and moral certainty, is destined for more than mere day-to-day survival. Tom undergoes the most significant transformation in the novel as he sheds this carpe diem (seize the day) philosophy for a commitment to bettering the future.
During their journey west, Tom assumes the role of Jim Casy’s reluctant disciple. The former preacher emphasizes that a human being, when acting alone, can have little effect on the world, and that one can achieve wholeness only by devoting oneself to one’s fellow human beings. The hardship and hostility faced by the Joad family on their journey west serve to convert Tom to Casy’s teachings. By the time Tom and Casy reunite at the cotton plantation, Tom realizes that he cannot stand by as a silent witness to the world’s injustices; he cannot work for his own family’s well-being if it means taking bread from another family. At the plantation, Tom abandons the life of private thought that structures the lives of most of the novel’s male characters—including Pa Joad and Uncle John—and sets out on a course of public action.