There are three such unities: the unity of time, the unity of place, and the unity of action.

The unity of time means that everything takes place within a space of twenty-four hours or fewer. From the time that Oedipus greets the priest and suppliants who have come with prayerful offerings to the palace of Thebes to the time Oedipus learns the truth about his own parentage, blinds himself, and is exiled, everything takes place within this limited time frame.

The unity of place means that there is just one setting for the entire text. In this case, it is the steps outside the palace. Here, Oedipus greets the suppliants, receives news from the oracle, and so on. Note that Oedipus does not go to the oracle himself but sends Creon. Oedipus has Tiresias, the blind prophet, brought here to him for questioning. No time is lost in travel, and no distractions are created by having the main character traverse these distances. Of course, some events—especially the violent ones (Jocasta's suicide, Oedipus blinding himself with her brooches)—takes place, by convention, off-stage, but someone always comes to this same place to report what has happened elsewhere.

Finally, the unity of action means that the entire subject matter of the text is focused on Oedipus's search for Laius's killer and the subsequent consequences of that search. The priest and suppliants come as a result of the terrible plagues that have beset Thebes, which are the result of the fact that Laius's murderer is still free and unknown; thus begins the search for his murderer. Everything that takes place after this revolves around this search.

All three of Aristotle’s dramatic unities—at least as they were interpreted by French classical dramatists—are present and correct in Oedipus Rex by Sophocles. Aristotle was a great admirer of Sophocles’s masterpiece and regarded it as a paradigm of how a play should be constructed.

First of all, we have unity of time. The action of the play takes place over the course of a single day. As with the other two unities, this ensures that there is complete economy of expression. No time is wasted in presenting the events as they unfurl on stage. The unity of time means that the audience is concentrated purely and solely on the here and now, as that’s the main focus of the drama.

We also have unity of place. In keeping with the traditional conventions of Greek theater, the action of the play unfurls in one single place, namely the royal palace of Thebes. This means that Oedipus Rex effectively consists of one long scene, which, as with the unity of time, keeps the audience’s concentration firmly fixed on what’s happening right in front of them.

Last but not least, we have the unity of action. There is just one plot—no subplots, no comic relief. Nothing, in fact, that might detract the audience’s attention from what really matters. Even so, the unity of action, like the other two unities, cannot of itself constitute a great play. All that these unities can do is to provide a dramatic structure which the playwright then builds upon, using his or her skills.

While the "Unity of Place" was simply the necessity of construction for the Greek stage, the only unity that Aristotle insisted upon was the "Unity of Action" although he did state that tragedy must keep its action "within one revolution of the sun," implying that "Unity of Time" is also a requisite to tragedy.

Unity of Place

The action of Oedipus Rex by Sophocles centers around Thebes where the city has been beset with plagues, famines, and fire. As king, Oedipus promises to seek the reason for these punishments; in so doing, he learns that the gods have reacted against the murder of their previous king, Laius. And, tragically, it is revealed that Oedipus has been the murderer. Oedipus punishes himself by blinding himself; then, he has Creon order his exile. ending the play, however, with Oedipus being led into the palace.

Unity of Time

The plot of Oedipus Rex does keep its action within Aristotle's "one revolution of the sun." For, the incidents that lead to the tragedy-- the prophecy that causes Laius and Jocasta to give up their son, the discovery of the baby Oedipus, and the murder of Laius--are all outside the drama proper. It is only the attempt to learn the cause(s) of the problems in Thebes that concerns the drama.

Unity of Action 

All the action of the drama proper revolves around the attempt of Oedipus to find a remedy for the terrible occurrences in Thebes.  He sends his brother-in-law Creon to the Oracle of Apollo in Delphi to learn what causes the fire, famine, and plague in Thebes.  When Creon returns, Oedipus begins his investigation of the death of his predecessor, Laius.  Of course, he learns his own involvement in this death and the consequences of his actions.

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In his Poetics, which has become the consummate guideline for tragedy, Aristotle praises Oedipus Rex for having an exemplary, well-constructed plot that takes place with one full day; in addition Aristotle contends that Sophocles's play is one which is capable of inspiring fear and pity not only in its audience but especially in those who have merely heard of the story.  And, part of this impact upon audiences is due to the play's unity of action, as well as unified time and place.