Ivan's basic nature is defined early in the novel when he is depicted as being a very independent child. He is, in contrast to his brother Alyosha (who freely accepts help and aid from other people), unable to receive freely any act of generosity.
By nature Ivan is a very studious person who has strong intellectual inclinations, qualities that later dominate his personality. As a result, we come to know Ivan through his thoughts rather than through his actions; in other words, his intellect defines his essential nature.
As an adult, Ivan seldom speaks, and then only to individuals who seemingly are intellectually capable of understanding his complexities. When he accompanies the others to the monastery, for instance, he is quiet and reserved; he waits to talk until someone begins to discuss Ivan's article, written while he was still at the university. This article is a key to Ivan's makeup. He is an atheist, yet concerned with the fate of mankind on this earth; all of his studies have led him to a deep compassion for the sufferings and tribulations of earthly man. But he cannot honestly accept religious matters on faith alone. That which does not conform to human logic is unacceptable to him. Unlike Alyosha, he cannot accept the abstract theory of God's mercy and goodness because he has seen too many examples of injustice and suffering in the world. He refrains from questioning the existence of God but refuses to accept this world as being God's world. Ivan feels that a God who is infinitely good and just should have created a world where there is no innocent suffering. Nor can he accept the idea that all innocent suffering is a part of a great plan because God gave unto man a human mind, and any theory concerning God's justice must be understood by this God-given mind. Sadly, logic cannot explain the long history of human suffering.
From his questionings, then, Ivan has developed a long prose poem entitled "The Grand Inquisitor" in which he envisions Christ returning to earth. He is again threatened with death, but this time He is indicted by the church. Christ's second death is demanded because the cardinal explains that mankind is too debased to accept the ideas advocated by Christ. The church, consequently, has taken away the freedom that Christ promised man, and for man's good it has enslaved him. In this poem, Ivan reveals the depths of his compassion for mankind, creatures who he feels do not have the strength to follow the strenuous demands made by Christ.
Ivan supports a general acceptance of Christian morality because he feels that if the average man does not have some type of dictate to follow, an era of lawlessness ensues. Faith in immortality and a healthy fear of retribution are great deterrents to crime, Ivan believes, for with no immortality, logically "anything is allowed." It is this statement, which Ivan expresses to the servant Smerdyakov, that leads to the murder of Fyodor Karamazov. Smerdyakov, convinced that anything is permissible if there is no divine retribution, feels free to commit any act; he chooses parricide.