According to Frederick I. Carpenter in his essay, "The Philosophical Joads," Steinbeck's social thought seems to be shaped by three distinct strands of nineteenth century American philosophy: the Emersonian concept of the Oversoul, the idea of a humanism expressed by the love of all persons and the embracing of mass democracy found in the works of Walt Whitman and Carl Sandburg, and the pragmatism of Henry James.
The Transcendental concept of the Oversoul is expressed in the earthy folk language of Jim Casy as the belief that all human's souls are really just part of one big soul. Ralph Waldo Emerson, the most well known proponent of transcendentalism, defined the Oversoul as the universal mind or spirit that animates, motivates, and is the unifying principle of all living things. Casy makes numerous references to this one large soul that connects all in holiness, and they dovetail nicely with the basic idea of strength in group unity. Somewhat conversely, American transcendentalism also recognized individualism, a faith in common people and their self-reliance. This concept of the survival of the human life force is symbolized by the survival of the land turtle and Ma's comment, "We're the people — we go on." This combination of rugged individualism and an embracing of all men as part of the same Great Being is physically expressed in the education and re-birth of Tom Joad: His strongly individual nature gives him the strength to fight for the social welfare of all humanity.
The movement of the major characters in the novel from a religious-based to a humanity-based philosophy of life supports the concept of humanism found in Steinbeck's social theory. This thought reflects the political ideals of the nineteenth century American poet, Walt Whitman, who believed that democracy was based on the existence of a mutual connection between individuals, a situation in which the group entity was of as great an importance as the individual. Humanism can be traced back to Whitman's exaltation of the common man and can best be understood as a love of all persons. This is the spirit that Jim Casy is referring to when he claims that it's "all men and women that we love
the Holy Sperit — the human sperit." This love will most often be physically expressed by the mother figures in the novel: Ma, Sairy Wilson, and eventually, Rose of Sharon. From her first appearance in the novel, Ma is the epitome of the concept of loving one's neighbor. She is the first to extend comfort or nourishment to strangers. This willingness to help people is seen in her welcoming of Casy into the family and her feeding of the hungry children in the Hooverville camp. She works selflessly for others and tries to instill the same attitude in Rose of Sharon. Sairy Wilson's compassionate help during Granpa's death, in spite of her own illness, is another example of human love extending outside the family. Rose of Sharon is slow to embrace this selflessness and giving, focusing instead on her own comfort and well-being for the majority of the novel. In the end, however, she, too, becomes part of this embracing of all humankind when she offers her life-giving milk to the starving stranger.
The third strand of Steinbeck's philosophy is pragmatism, what the author himself has termed "non-teological" or "is" thinking. Pragmatism holds that life should be viewed as it is, not as how it ought to be. Accordingly, one needs to live in the moment, reacting to what is happening in front of them based on their life experience and personal judgment, not on religious or moral teachings. Tom's responses to most situations are highly pragmatic, focused on "doing" as opposed to seeing or thinking. He is frustrated by Casy's broad musings on the future, preferring to "lay [his] dogs down one at a time" and "climb fences when [he] got fences to climb." He imparts this attitude to Ma, cautioning her to "Jus' take ever' day." Ma, however, is a pragmatist in her own right, but her pragmatic focus is on keeping her family together. When Al asks whether she is thinking about life is California, she is quick to reply that the others depend on her thinking only of their safety and comfort. Completely understanding her role in the family, she takes each setback as it comes and modifies her actions according to whatever situation confronts her. This ability to be flexible is another aspect of pragmatism, an ability that Steinbeck feels is fundamental to the survival of the migrant workers. Pragmatism also includes a movement away from abstract religious beliefs, concentrating instead on the holiness of those who are living. Casy's acceptance of this belief is seen in his abandonment of formal religion and prayer. His comments at Granpa's grave, that those who are living need help, support his pragmatic attitude.
The theory of Jeffersonian agrarianism was later recognized by critic Chester E. Eisinger to be the fourth strand of Steinbeck's social philosophy. Agrarianism is a way of living that is intricately tied to one's love and respect of land. Through connection with the growth-cycle of the land, humankind gains identity. Steinbeck's symbolic treatment of this idea can be found repeatedly in The Grapes of Wrath. Steinbeck uses the life force in a horse and the mechanized power of the tractor to metaphorically contrast the productiveness that comes from a love of the land with the deadness that arises from an isolation from it. Men are whole when they are working with the land, and conversely, they are depleted, emotionally and physically, when they are taken from the land. Losing the farm "took somepin' outa Pa," and one displaced tenant states, "I am the land, the land is me." When that land is taken away, the men lose part of themselves, their dignity, and their self-esteem. Also closely tied to the land is family unity. With the separation from the land comes a disintegration of the family unit. Ma expresses this most succinctly when she observes, "They was the time when we was on the lan'. They was a boundary to us then.
We was the fambly — kinda whole and clear. An' now we ain't clear no more."