What are the themes in Synge's, Riders to the Sea?
The dominant theme of Synge's, Riders to the Sea, is fate. The tragedy plays off of ancient Greek tragedies which also deal with fate, such as the tragic drama of Oedipus. (The name of the character, Maurya, for instance, is a variant of the Greek word for tragedy. The play opens with Cathleen spinning at the spinning wheel just as the Fates do in Greek myth.) Fate in the play is determined by the sea. The Irish peasants are helpless against the natural force that every male must contend with in order to provide for himself and his family: the sea. The sea is more powerful than God and the priest, and it alone determines the peasants' fates. There are only two riders to the sea in the play, one already doomed and the other soon-to-be doomed.
One might be tempted to elaborate and speak of Irish poverty, Irish rural life, the love between a mother and her men, etc., but essentially Synge mixes Irish folklore with Greek myth to create a tragedy that reveals natural forces dominating the fates of helpless humans.