Leaving Alyosha, Ivan feels morose and dejected, emotions probably related to the guilt that he feels by associating with Smerdyakov. For even though Ivan does not realize it, he is subconsciously beginning to feel a certain duplicity in his relationships with the servant; the last two chapters, in particular, show how certain actions on Ivan's part implicate him in the murder of old Fyodor.
This fact is also important: Ivan feels a distinct loathing for Smerdyakov. He has entered into many philosophical discussions with him, and we learn that they have discussed such questions as how there "could have been light on the first day when the sun, moon, and stars were only created on the fourth day." Smerdyakov, in turn, has discussed things that would impress Fyodor, hoping to make an impression on him and contradict old Grigory. However, he has, we discover, taken most of his ideas from Ivan. Even the idea of the murder came from Ivan.
When Ivan meets the cook, he has planned to say to him, "Get away, miserable idiot. What have I to do with you," but instead he says, "Is my father still asleep?" This reversal suggests that Ivan is repulsed by this creature but is drawn to him at the same time. By the same analogy, Ivan is repulsed by the idea that his father will be murdered but seems also to acquiesce in readying the scene for the hypothetical murder.
