“It's not that I don't accept God, Alyosha, I just most respectfully return him the ticket.”

This quote of Ivan’s in the fourth chapter of the fifth book establishes Ivan as an atheist or nonbeliever, his reasoning for being so, and his opposition to his brother, Alyosha. Ivan is presented as the most intelligent of the three Karamazov brothers. He is driven by curiosity and logic, refusing to acknowledge the existence of that which cannot be proven. Ivan’s intelligence and curiosity have plagued him to a point of conflict as he cannot understand the thing he most desires to know, which is the reason for human suffering. Is it his own fault and the fault of his fellow man? Or is it the fault of God? Although Ivan does not believe in God, he tells Alyosha in this moment that if God were real he would reject him, as he feels God has shirked his duty to end human suffering. 

“I think the devil doesn't exist, but man has created him, he has created him in his own image and likeness.”

Because Ivan does not believe in God, he is forced to confront mankind as being responsible for the world’s suffering. This quote from Book 5 illustrates Ivan’s perspective. He views men as devils not only capable, but uniquely prone, to cruelty. This view, in light of Ivan’s intense curiosity and intelligence, sets the stage for his great internal struggle throughout the novel. Ivan cannot make sense of how man, including himself, can be responsible for one other’s crimes. And yet, it is his only explanation. After Smerdyakov confess to Ivan that he killed Fyodor and blames Ivan for inspiring him to do so, Ivan reaches a breaking point in terms of this conundrum. He cannot shake the guilt Smerdyakov has placed upon him, a guilt which has been building throughout the novel, and begins to suffer from mental collapse.

“The more stupid one is, the closer one is to reality. The more stupid one is, the clearer one is. Stupidity is brief and artless, while intelligence squirms and hides itself. Intelligence is unprincipled, but stupidity is honest and straightforward.”

Although Ivan possesses extreme intelligence, he does not see such intelligence as a gift. This quote from Book 5 is an example of the ways in which Ivan feels plagued by his intelligence and curiosity. Intelligence does not enable Ivan to ignore his conflicting perspectives on humanity. Stupidity would allow him to let go of the unanswered questions that plague him. Ivan blames his quest for answers for the guilt he feels about the part he plays in the suffering of mankind, and he feels that if he possessed less intelligence, he would not be so conflicted.