The Land
Steinbeck utilizes the opening chapter's symbolic landscape to illustrate the overriding theme of good versus evil that permeates the novel: the Eden-like Salinas Valley is surrounded by the "good" sunlit Gabilan Mountains to the East, and the dark and foreboding "bad" Santa Lucias Mountains to the West. For most of the novel, the characters reside in this valley.
The land also reveals the characteristics of the two major families, the Hamilton and the Trasks. The Hamiltons settle in the driest land, but although their land is practically barren, they raise nine children. The wealthy Trasks buy the most fertile land, but despite its rich soil and plentiful water, the farm remains uncultivated for decades after Cathy abandons Adam.
Good vs. Evil
Steinbeck illustrates the central theme of good versus evil through two of his primary characters: Samuel Hamilton, who represents goodness, and Cathy Ames, who represents pure evil. Both characters play crucial roles in the spiritual development of the protagonist, Adam Trask.
Samuel Hamilton, the positive patriarch, mentors Adam with support and guidance, unlike Adam's own father, Cyrus, who lies about his military record to amass a fortune. Samuel, an Irish immigrant himself, views books as treasures, and fathers nine children. Throughout the novel, he is associated with light, water, and fertitility.
Cathy Ames is Samuel Hamilton's polar opposite. She murders her parents, becomes a prostitute and brothel owner, enslaves her whores with drugs, encourages sadomasochistic sexual practices, and blackmails her customers. In contrast to Samuel, Cathy is associated with darkness and gloom.
Both the innate goodness of Samuel Hamilton and the inherent evil of Cathy Ames deeply influence Adam Trask, and throughout the novel he wavers between the two poles. He loves his wife Cathy even when he is confronted with her evil nature, but also deeply admires his teacher and mentor, Samuel.
Timshel
The concept of timshel is a major thematic concern throughout the novel. A hebrew verb, timshel translates into "thou mayest", and expresses the notion that humans have the ability to choose good over evil. It holds that we can decide not to be influenced by our dark family histories, and choose instead to live more positive lives.
The concept of timshel stipulates that every individual, at any given time, has the ability to choose good over evil. This idea is particularly pertinent at the end of the novel, during Adam's death scene. Adam's son Cal believes that he is condemned to become an evil man because he has inhertited his prostitute mother's innately evil nature. Adam, however, raises his hand in blessing and utters the word to his son - timshel - signifying the fact Cal can decide his own moral destiny for himself.
Sibling Rivalry
Steinbeck employs the theme of rivalry to the relationships between the novel's two sets of brothers: Charles and Adam, and Cal and Aron, whose initials recall the biblical brothers Cain and Abel. The sons of Adam and Eve, Cain is a farmer and Abel a shepherd. God prefers Abel's sacrificial offering of a lamb over Cain's offering of grain. In a jealous rage, Cain murders his brother. Cain angrily replies to God's inquiry by saying, "Am I my brother's keeper?" Cain is exiled to wander in the East of Eden.
Charles and Adam's lives and actions recall those of Cain and Abel. When Cyrus favors Adam's birthday gift over Charles', the jealous Charles nearly kills Adam. The next generation of brothers, Cal and Aron, further perpetuates the Cain and Abel legend. When their father, Adam, spurns Cal's birthday present of $15,000, the jealous Cal takes revenge on Aron by taking him to see their mother, a prostitute. Aron joins the army, and soon after dies.
Fatherhood
Steinbeck creates two important father figures in the novel: Samuel Hamilton and Cyrus Trask. Both of these father-figures influence the protagonist, Adam Trask, and present him with paternal models for the choices he must make in his own life. Both Samuel and Cyrus are bearded, in the biblical patriarchal style.
Adam's father, Cyrus, commits the novel's original sin by lying about his Civil War record to advance himself politically and financially. Samuel, on the other hand, is the archetypical force for goodness - the good father to Cyrus' bad father. He exhibits enormous physical strength and capability, while Cyrus hobbles on one leg. Samuel is a symbol of life, of fertility: he cultivates barren soil, fathers nine children, and is associated with water imagery. He digs wells, is always washing, and delivers the twins, Aron and Cal.
Cyrus, on the other hand, is a negative force: a cruel, one-legged thief, Cyrus continually manipulates those around him. He is associated with disease and death, rather than fertility. He infects his religious wife with syphilis, causing her to commit suicide.
Truth
Throughout East of Eden, characters withold the truth both from themselves and from others. Cyrus lies about his Civil War record to win an important job and an ill-gained fortune. Charles withholds the truth about Cathy's seduction on Adam's wedding night. Lee lies to himself about his desire to leave the Trask family and open a bookstore. Cal keeps his business ventures secret from his father. Adam and Lee keep the truth about their mother, Cathy, from Cal and Aron. Similarly, Cal fails to inform his father and Lee that he knows that his mother is a notorious brothel owner. Adam lies to himself about Cathy and excuses her depraved behavior.
However, the truth ultimately sets Adam and Cal free. Cathy, the ultimate liar, is suspicious of Adam when he arrives to inform her that Charles has left her a large inheritance. She is used to dealing with people who lie. When he finally faces the truth about her, he feels exhilarated and free. When Cal faces up to the fact that telling Aron the truth might have resulted in his death, he takes responsibility for his actions, and realizes that he has the ability to make good choices in the future.
The Sins of the Father
Throughout the novel, Steinbeck questions the biblical statement that the sins of the father are visited upon the son (Psalms 79:8). Early on, Cyrus Trask lies about his military record in the American Civil War to gain an important government position in Washington D.C. When he dies, he leaves his children, Charles and Adam, an ill-gained fortune. It might seem that Charles and Adam are doomed to live difficult lives because of their father's original sin. Indeed, Charles lives a miserly existence as a laboring recluse on the New England family farm and never knows a moment of happiness, while Adam, too miserable to return home, wanders as a vagabond and marries the ultimate evil female, Cathy Ames.
Cyrus's sin does indeed seem to have filtered down to the next generation. The deeply devout Aron attempts to escape his legacy, but death comes early, on a battlefield in France during World War I. Cal, it seems, is similarly doomed to immorality by his mother's depraved spirit - he earns $15,000 by taking advantage of farmers during the war. He blames himself for his brother's death until Lee helps him understand that God gave people the ability to choose goodness over evil. Cal can undo the family curse and live a morally upright life.
