In short, the truth of the matter was Nippers knew not what he wanted. (9)
Nippers's profound discontentment is a result of his uncertainty and undirected ambition – we must wonder if Bartleby is happier, in his way, than the unsure Nippers.
"I would prefer not to," said he.
I looked at him steadfastly. His face was leanly composed; his gray eyes dimly calm. Not a wrinkle of agitation rippled him. Hat there been the least uneasiness, anger, impatience or impertinence in his manner; in other words, had there been anything ordinarily human about him, doubtless I should have violently dismissed him from the premises. But as it was I should have as soon thought of turning my pale plaster-of-Paris bust of Cicero out of doors. (22)
Bartleby's decision is so decisive that it's inhuman – his choices are so definite that his mind is unchangeable, a quality that makes them impossible to question.
"I prefer not to," [Bartleby] replied in a flutelike tone. It seemed to me that, while I had been addressing him, he carefully revolved every statement that I made; fully comprehended the meaning; could not gainsay the irresistible conclusion; but, at the same time, some paramount consideration prevailed with him to reply as he did. (27)
Here, the Narrator tries to comprehend the incomprehensible: Bartleby's decision-making process.
"Why, how now? What next?' exclaimed I, "do no more writing?"
"And what is the reason?"
"Do you not see the reason for yourself?" he indifferently replied. (70)
Bartleby's justification for his decision to stop working is something that he finds apparent, even though his employer does not; honestly, we're with the Narrator here in not quite being sure about what the scrivener means.
[Narrator:] "The time has come; you must quit this place; I am sorry for you; here is money; but you must go."
"I would prefer not," [Bartleby] replied, with his back still towards me.
He remained silent. (76-77)
It's pretty clear from this interaction (and all those previous) that Bartleby's choices are not governed by anything but himself, even external force.
[Bartleby:] "I would not like it at all; though, as I said before, I am not particular." (114)
This new addition, "I am not particular," is one of Bartleby's strangest pronouncements yet. By claiming that he's not picky, does he mean to say that he hasn't been making negative decisions all along, and has simply been hanging out, waiting for the right thing to come along – the thing he would "prefer" to do? That's kind of what it looks like.
Strangely huddled at the base of the wall, his knees drawn up and lying on his side, his head touching the cold stones, I saw the wasted Bartleby. But nothing stirred. I paused, then went close up to him, stooped over, and saw that his dim eyes were open; otherwise he seemed profoundly sleeping. Something prompted me to touch him. I felt his hand, when a tingling shiver ran up my arm and down my spine to my feet. (128)
Is Bartleby's death suicide? Or did he simply die because he could not continue living in prison? We learn from the grubman that Bartleby continued to prefer not to eat anything…do you think he consciously chose to die?