Foreshadowing is a literary technique in which an author hints at a later development in a story through an earlier element of plot, character, dialogue, or setting. The hint may be quite strong or rather subtle, but when we encounter the later development, our minds jump back to what happened or what was said before and we recognize the connection.
The foreshadowing in August Wilson's play Gem of the Ocean is quite subtle. There are no big “Ah-ha! So that's what that meant!” moments, but if we stop to reflect, we can see how later developments in the play reflect earlier events and how earlier events have given a nod to later occurrences.
When the play opens, the characters are talking about a man named Garret Brown who jumped into the river and drowned rather than falsely admit that he had stolen a bucket of nails from the mill. His principles and his devotion to the truth are more important to him than his own life. Garret Brown foreshadows another character in the play, Solly Two Kings. Like Garret, Solly stands by his principles even though it costs him his life. Unlike Garret, however, Solly is guilty of a crime, for he really does set fire to the mill. Even though he is very close to escaping to freedom, he decides at the last moment that he just can't do it. As Citizen explains, Solly said "he didn't feel right being free and the rest of the people in bondage" (85). So Solly goes back to face the consequences of his actions, and Caesar shoots him.
Even Caesar's brutal actions against Solly are foreshadowed. Caesar shoots at Garret even as the latter struggles in the water. Also, according to Black Mary, Caesar's trigger-happy behavior extended even to shooting and killing a young boy who had taken a loaf of bread from Caesar's bakery. With precedents like that, how can we not expect Caesar to kill Solly when he catches up with him?
Finally, foreshadowing occurs again when Aunt Ester has a dream about Solly. "I dreamed you had a ship full of men and you was coming across the water," she tells him (19). In the dream, Solly's boat sinks, and all his men are lost, but Solly tells Aunt Ester that he will get another boat and more men. When Citizen undergoes a symbolic crossing of the water to wash his soul, we learn that such a crossing is a metaphor and image for death. Aunt Ester's dream hints, again subtly, at what will happen to Solly. He will, at the very least, be in great danger, and he plans to cross the water, even though he is delayed. Of course, it turns out that Solly is in great danger and that he is delayed in crossing the water (by his near escape) but actually does so in the end when he dies at Caesar's hand.