Who do you hold the most responsible for Simon’s death: Ralph, Jack, Simon, or the group as a whole?
From the very beginning, Jack takes the early initiative in leading violent acts while on the island. At first, the acts are directed toward the pigs under the presumption of obtaining food, but by chapter 3, Jack already seems to be turning more toward the idea of killing in general, less directed at food specifically:
He tried to convey the compulsion to track down and kill that was swallowing him up.
"I went on. I thought, by myself--"
The madness came into his eyes again.
"I thought I might kill."
Simon, seen apart from the violence of the group and frequently interacting with nature, is Jack's foil. The younger children are drawn to him, and he is seen as a helper to the other boys. Where Jack seems singularly minded on killing and bloodshed, Simon asks deeply introspective questions and makes keen observations. In chapter 5, for example, he notes that maybe this "beast" they fear "is only us."
This sets up a key conflict in the novel: a quest for violence versus a quest for knowledge. Although Jack and Simon don't engage in physical conflict before Simon's death, the fundamental ideas they represent create the conflict that leads to Simon's death.
Simon discovers that the beast the boys fear is "harmless and horrible" and seeks to inform the other boys (chapter 9). Unfortunately, when he meets the boys, they are in a frenzy of bloodlust and see him as the beast they fear. Symbolically, the boys fear Simon's innocence and goodness, and Jack's thirst for blood drives the group to violently slaughter Simon.
While an entire group of boys takes part in the murder, it is Jack's leadership that drives them in this direction. The boys submit to his power and guidance and see what he sees—that Simon is a beast who must be killed. Without Jack's influence, the boys would almost certainly never have chosen to murder Simon.
Simon's death may be considered to be the climax of the novel as it comes with such high drama amidst the boys whipping themselves into a frenzy as they dance and chant their 'song' in a terrible storm.
Certainly at first glance Simon's death could be attributed to Jack. It was he who had encouraged the boys to shed all the binds of civilized behaviour and to celebrate the act of killing and spilling of blood. He had spurred the boys on to the point where a dangerous mob mentality had developed; so powerful that even the most sensible of the group (Ralph and Piggy) were sucked into its bloodthirsty excitement. Jack was very much at the centre of this, "...and Jack, painted and garlanded, sat there like an idol." (p. 183).
To a lesser extent it could be argued that Ralph's failure of leadership led to such a chaotic scene on the night of Simon's death. Had he been a more decisive, better organized leader able to stand up to Jack's impetuous nature earlier on then perhaps the group of boys would have stayed united and the whole tragedy could have been avoided. Certainly it is hard to apportion blame on Simon himself as he was only bursting with desperation to bring the truth of 'the beast' to the entire group.
In the final analysis it was of course the whole group who so brutally mauled Simon to death. However, mobs are inevitably ugly, and a group of young boys in a setting knowing no adult supervision and instead succumbing to the base instincts of a despot peer (Jack) would of course be a highly dangerous social situation.
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