What role does superstition play in Riders to the Sea?

Superstition is an inordinate belief in supernatural causation that exceeds rational bounds. Sometimes people become superstitious after a series of unfortunate events occur because they feel there must surely be some causation to these occurrences.

Such is the case with one of the main characters of Synge's one-act play, the character named Maurya. After the misfortunes of having lost six of her sons, this mother now believes that something will happen to her son Bartley. Further, her fears create suspense in the narrative of the play and generate apprehension in the audience, as well.
Because of her fears, Maurya does not want her son Bartley to travel on the sea, and she has even asked the local priest to talk with him. Nevertheless, Bartley insists upon departing, sailing with two horses to the mainland where he will travel to a fair in Galway in order to sell these horses. Before he departs, Maurya cries out as Bartley stands in the doorway:

He's gone now, God spare us, and we'll not see him again. He's gone now, and when the black night is falling I'll have no son left me in the world.

Maurya expresses a superstitious fear that she will lose Bartley because six of her other sons have died on the sea. She also attributes supernatural powers to the sea that "takes" her sons from her.

Previously, Maurya's daughter Cathleen and her little sister Nora have talked about the last son's (Bartley's) departure for Galway; in this conversation, Cathleen asks Nora if she has talked with the priest about stopping Bartley because of the turbulent weather. Nora tells her sister what the priest has said,

"I won't stop him," says he, "but let you not be afraid. Herself does be saying prayers half through the night, and the Almighty God won't leave her destitute," says he, "with no son living."

To some, the priest's faith in prayer may seem rather superstitious as he places excessive credibility in supernatural intervention because of Maurya's prayers.

The images that Maurya creates as she describes her vision of the

...fearfulest [sic] thing any person has seen, since the day Bride Dara seen the dead man with the child in his arms

generate a terrifying tone in the narrative.

Later on, Maurya describes a vision that she has seen:

Bartley came along, and he riding on the red mare with the gray pony behind him....and there was Michael upon it with fine clothes on him, and new shoes on his feet.

Believing her vision to be a supernatural omen, Maurya predicts that Bartley will be lost at sea. Tragically, she is right.

Clearly, superstitions play a key role in the narrative of Riders to the Sea as they generate the mystery and suspense which add to the overall effect of the drama.