Obviously there are two ways of thinking about Oedipus and his fate in Oedipus Rex by Sophocles. One idea is that he was a victim of fate, powerless to make any decisions on his own. In this scenario, his choices were in fact preordained acts over which he had no control. Another idea suggests that Oedipus is a man who makes his own choices and is therefore the master of his own destiny. This is the great tension of the play, and it all hinges on the prophecies which were made both to Laius and Jocasta and to Oedipus.
The prophesy Oedipus receives is that he will kill his father and marry his mother, and he has no intention of doing those things so he runs away. When we consider whether Oedipus could have changed his fate, the simplistic answer is that he could have avoided killing anyone or marrying anyone if he wanted to be absolutely certain the prophecies did not come true. Instead he gets angry and kills Laius and accepts Jocasta as his bride for ridding Thebes of the Sphinx. To that extent, then, he had free will; however, it does seem a bit more complex than that.
Jocasta scorns fate when she points out that the oracles predicted that her son would kill her husband and marry her, and obviously, she boasts, that has not happened. When she discovers the truth, that things happened just as the oracle predicted they would, she immediately kills herself. This is a clear indication that she thought she was in control of her life but was instead a mere victim of fate.
Oedipus, too, believes he can outmaneuver fate (like mother like son?) and immediately leaves Polybus and Merope so he will not kill the one and marry the other. What he does not know (and the oracles obviously do know) is that those two are not his real parents. Later, when he tries to find out what is cursing his beloved Thebes, Oedipus learns from the blind prophet Teiresias the truth that he is the curse and what the oracles decreed has come to pass. The gods knew what Oedipus did not. When he finds out the truth, he blinds himself and begs Creon:
Cast me out as quickly as you can,
away from Thebes, to a place where no one,
no living human being, will cross my path.
In both cases, however, there is an element of free will. When Jocasta learns the truth, she has a choice about how she will react to it. She exercises her right to choose by killing herself. When Oedipus begins his search for the truth, that is his choice; and when he chooses to blind himself and be ostracized after he discovers it, he is exercising his free will.
Also, both Jocasta and Oedipus claim not to believe in the prophecies, yet both of them belie that belief by taking drastic actions to try to thwart them. She sends her own son off to the mountains to be killed, demonstrating her fear that the prophecy would come true. He runs away from his home without even saying goodbye to the people he assumes are his parents, demonstrating his fear that the oracles spoke the truth. Once he believes he has accomplished his goal, however, he refers to himself this way:
Who rank myself as Fortune's favorite child,
The giver of good gifts....
He believes he has cheated fate, but of course he soon learns the horrible truth, which happened just as the oracles decreed.
Clearly, then, Sophocles is demonstrating his belief in the supremacy of fate over self-determinism, though he does allow that we all have some degree of choice. We get to choose how we will react to the events fate has destined for us.
Fate is a common theme in Greek writing. The idea that attempting to avoid an oracle is the very thing which brings it about. "Oedipus Rex" is a Greek tragedy. Free will also plays a large part in "Oedipus Rex". Laius and Jocasta use free will to try to prevent the oracle's prediction. which says that Laius will be killed by his own son. To prevent the prophecy from coming true, they send him away to his death. However, there is free will in the shepherd's decision to give him to King Polybus and Merope. When Oedipus hears a rumor that he is not the biological son of Polybus and Merope, they choose to deny that it is true. Oedipus makes a choice to leave Corinth to prevent himself from killing Polybus, who he believes is his father and marrying Merope, who he believes is his mother. He chooses to head toward Thebes, where he encounters Laius. Oedipus chooses to kill the man, unknowingly killing his father and fulfilling the first part of the prophecy. He chooses to marry Jocasta, fulfilling the second part of the prophecy. In response to the plague at Thebes, he chooses to send Creon his brother-in-law to the oracle at Delphi for advice, resulting in an investigation of Laius' murder. None of these choices is predetermined.
When Jocasta learns that Oedipus is her biological son, she chooses to hang herself. Upon finding his dead mother, Oedipus uses the pins that held her dress together, and uses them to plunge into his eyes. All the actions were based on free will to avoid the prophecy. Then when the prophecy was fulfilled, the characters acted freely in their despair.