Raskolnikov kills the pawnbroker Alyona Ivanovna to find out whether he is an extraordinary man, one with the right to overstep the law, but the book places other reasons beside this one and leaves open which weighs most.
One is the money his family needs: his mother and sister sacrifice themselves for him, and the letter announcing Dunya's engagement to Luzhin pushes him. Another is an account he overhears in a tavern, in which a student says the old woman, rich and cruel to her sister, does not deserve to live: "One death and a hundred lives in exchange, why, that's arithmetic!" When the officer asks the student whether he himself would kill the old woman, the student answers that he would not, and Raskolnikov hears from a stranger the idea that had just been born in him.
When he confesses to Sonia, he offers several reasons and disowns each one: Napoleon, his mother and sister without resources, the louse. Two phrases remain: "I simply killed; I killed for myself, for myself alone." and "I needed to know then, and to know quickly: am I a louse, like everyone else, or a man?" The old woman would be the proof of a question about himself.
There is also the way the act happens. After the dream of the mare, he gives up; he overhears by chance the hour when Lizaveta will leave, and he feels the choice has been taken from him. The narrator says it was "as if he had caught a piece of his clothing in the wheel of a machine, and it began to pull him in." The text admits two readings: the real collapse of his will, or the use of chance to shift responsibility.