Through most of the play, as far as Oedipus is concerned, he isn't "struggling" with free will at all, he is acting upon it. However, once the real truth is unraveled, his free will and past actions based upon his own choices are revealed as his tragic flaw -- the hubris of believing that he could outsmart the gods and avoid the prophecy that he would "kill his father and marry his mother."
Oedipus Rex is a Tragedy in the true classical sense of the word, which means that Oedipus must be the architect of his own demise, not a victim of circumstance. This sets him up for a struggle with the pre-ordained oracle from the gods, suggesting that Oedipus, if we observe his actions as representative of the human struggle, is destined for his downfall because he attempts to act upon his own impulses (or free will), rather than acting in service to the gods.
So, it is Oedipus' false sense of free will that sets him up for tragic consequences in the following ways:
- He leaves the home of his assumed father, Polybus, when he learns that there is a prophecy that he will kill his father and marry his mother. He hopes to avoid this outcome by this action, not knowing that Polybus is his adopted father.
- While out on the road, he meets a man who is just as stubborn as himself and refuses to move and allow Oedipus to pass. In a rage, he kills this mysterious man (so like himself) -- the man later revealed to be his natural father, Laius.
- He next solves the riddle of the Sphinx and wins the hand of the widowed Queen of Thebes, Jocasta, and they marry. Later, he discovers that Jocasta was Laius' widow.
- And he finally learns the truth of his adoption, making the connection that Jocasta is, in fact, his mother.
Ultimately, it is Oedipus' attempt to rely upon his free will, rather than his struggle against it, that seals his doom. This Greek Tragedy follows the standard party line: No human can escape his fate as it is predicted by the gods, and woe to him that might attempt to do so! The force that Oedipus struggles against throughout the play is the will of the gods as made manifest through the prophecy about his future.
A key theme in this remarkable play is the conflict between fate and free will. In so many works of literature this is a massive issue, as characters try to exert their independence and self-determination, but at every stage are batted down by the hand of fate who takes their lives in a direction that they often do not want to go. In this play, we see this occurring in the way that the various prophecies and oracles impact the course of a man's life as opposed to the extent that he can shape his own life through his own actions. Unfortunately for Oedipus, this play illustrates the triumph of fate over free will. From the first entrance of Oedipus, we are presented with a man who genuinely desires to be the best king of Thebes that he can. As he seeks the truth that will destroy him and his reign, he ironically expresses his desire to be a good king and find the cause of the plague in language that speaks of self-determination:
Tell me, and never doubt that I will help you
In every way I can. I should be heartless
Were I not moved to find you suppliant here.
From Oedipus's perspective, again and again he is exerting his free will in doing his utmost to act and find the cause of the plague. Likewise, we see that Oedipus is reluctant, unwilling or unable to accept the oracles and prophecies that are given in the play. He ironically denounces Teiresias for being a blind man when he does not like what he says, and key perhaps to the plot of the play is his response to the oracle that predicts his own involvement in the death of Laius. Oedipus denounces the truth of this oracle, calling them "empty words," yet the action of the play shows the truth of prophecies and that what the gods have decreed will come to pass, and Oedipus is left frustrated and helpless at his inability to allow his free will to dominate against the powers of fate that are set against him.