Using quotes to support the points and consider the audience's response to the actions of the other characters.
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The whole point of the Inspector is to accentuate the fact that everyone is responsible jointly for her death. This is the idea of collective responsibility which is one of the main messages of an Inspector Calls. That everyone is responsible for each other and what people do has a knock on effect beyond what they realise. Each person may not have individually case her death, but together all the protagonists did.
I would start of by spending a paragraph proving mrs Birling was most responsible as she was the last straw which caused Eva's suicide. Eva came to her as a last resort and committed suicide just 2 weeks after Mrs Birling refused to help her. Remember to use several quotes to support this such as the Inspector pointing out Mrs Birling saw her just two weeks ago, the fact that Mrs Birling lied about recognising her because she realised she would be blamed and that it was Mrs Birling who convinced the other members of the charity not to help Eva.
My next paragraph would argue that Eric was most to blame. Eric was possibly the only member of the household to actually do something legally wrong; first he "forced himself" on Sheila, then he stole money from his fathers work. Argue that Eva commuted suicide because she was pregnant with Eric's baby who she couldn't afford to sustain. Also show how Mrs Birling originally puts all of the blame on Eric before realising that Eric was the perpetrator. Support all of this with quotes.
My last, and most detailed paragraph would focus on the fact that it was everyone's responsibility. The whole message Priestley is highlighting is that everyone has collective responsibility. Every one must care for everyone. This is a direct response to the capitalist notions of the time. This is shown by the fact that as Mr Birling in giving his whole speach about only being responsible for yourself, he is interrupted by "a sharp ring of the doorbell. Birling stops to listen." Then the Inspector enters and shows how everyone caring for themselves jointly caused a chain of events that led to Eva's death. Prove this using the many times the Inspector speaks about collective responsibility, in particular his pivotal final speech where he says things such as "we are members of one body" and "we are responsible for each other."
Then conclude, perhaps arguing that everyone was responsible but you personally feel that eric/Mrs birling/boiling etc was most responsible.
Hope this helps.
