One major difference is that Greek tragedies were performed as part of a public religious festival. In Ancient Greece, plays were events for the whole community, a way of binding everyone together through a shared sense of values and beliefs.
Modern tragedy, on the other hand, tends to speak more to the individual rather than the community as a whole. In this more atomized, socially fractured age, tragedy is largely presented through the trials and tribulations of an individual, often a non-heroic individual isolated from society in some way. From these characters' experience of tragedy, a more generalized picture of the human condition emerges; the universal is derived from the particular. Whereas in ancient Greek tragedy, it's the other way round. The characters on stage are the means by which universal values, already accepted and understood by the whole community, are reinforced.
Probably the biggest difference between a modern tragedy and a classic Greek tragedy is the tragic hero....
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