In An Inspector Calls, the theme of responsibility is closely connected to those of social class and generational differences. While Mr. and Mrs. Birling show little concern for Eva's tragic fate because her misfortunes should be expected of "a girl of that class" -i.e. the working class- their children feel touched by the part they may have played in driving her to suicide.
Priestley's socialist ideas underlie these issues. The play seems to point at the fact that perhaps the younger generation will be more open to the notion of equality than are the elders. Mr. and Mrs. Birling, comfortably established at the top of the economic ladder, seek to move up the social ladder through Sheila's marriage to Gerald Croft, an aristocrat. However, they deny Eva the right to both social and economic mobility.
Another important theme is time, a subject whose nature fascinated Priestley to the extent that he experimented with it in many other plays (Dangerous Corner, Time and the Conways, I Have Been Here Before.) At the end of the play you wonder whether the action has taken place in the characters' minds, or whether it is a premonition, something that could be avoided if there were time to make changes in the causal chain of events unraveled by the Inspector's presence. In fact, has the Inspector been there at all? Does time go round in circles? If so, will the last ring of the doorbell be in fact the second in an endless repetition of the same event?
Although the characters are extremely interesting, this is mainly a play of ideas. Priestley takes a very clear stand about the first three themes discussed here, but leaves it to the spectator/reader to decide about the problem of time.