How does Oedipus Rex by Sophocles adhere to the classical unities?

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.

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.

Does Oedipus Rex observe the three unities?

Any discussion of the "three unities" in Oedipus Rex invariably includes reference to Aristotle's Poetics as the source of those unities.

In Poetics, Aristotle emphasizes only one unity—the "unity of action"—as absolutely essential to a tragedy.

Aristotle defines a tragedy as " an imitation of an action that is serious, complete, and of a certain magnitude" (Poetics, VI).

The important word regarding the "unity of action" is "complete," meaning that the plot should be self-contained, with a beginning, middle, and end, and that:

the plot, being an imitation of an action, must imitate one action and that a whole, the structural union of the parts being such that, if any one of them is displaced or removed, the whole will be disjointed and disturbed (Poetics, VIII).

It [a tragedy] should have for its subject a single action, whole and complete, with a beginning, a middle, and an end. It will thus resemble a living organism in all its unity (Poetics, XXIII)

In other words, a tragedy has a single, unified plot and no subplots.

Aristotle mentions the "unity of time" only in passing, as an observation, not as a rule.

Tragedy endeavors, as far as possible, to confine itself to a single revolution of the sun, or but slightly to exceed this limit. (Poetics, V)

Aristotle doesn't mention "unity of place" in Poetics at all.

The "three unities" as we understand them are derived from Aristotle's Poetics by French classicists in the seventeenth century. They believed that all serious French dramas should conform to the unities of time, place, and action—a single action occurring in a single place and within twenty-four hours, period.

In time, even these rules were loosened to allow scenes to occur in other locations that could be reached in twenty-four hours.

Nevertheless, Sophocles worked within these three unities in his tragic play Oedipus Rex, although he, like many other playwrights of his time, "pushes the edge of the envelope" regarding each of the unities.

Realistically, in terms of "unity of time," there aren't enough hours in a "single revolution of the sun" to accommodate everything that happens in Oedipus Rex.

Teiresias lives on Mount Telphosion in an area of ancient Greece called Boeotia, approximately twenty miles from Thebes. Oedipus has Creon send for Teiresais, twice and complains about what's taking him so long to get to Thebes:

OEDIPUS. Here too my zeal has nothing lagged, for twice
At Creon's instance have I sent to fetch him,
And long I marvel why he is not here.

Teiresias isn't there yet because he's an old blind man who needs a boy to lead him the twenty miles from his home to the palace, a journey that would easily take a full day for young, sighted man. For Teiresias and the boy—factoring in meal breaks, bathroom breaks, and occasional naps—the trip could take two days or more.

Later in the play, Oedipus sends for the herdsman who took the baby Oedipus to the mountains to die, but nobody knows for sure where he is:

JOCASTA. [A]s soon as he [the herdsman] returned and found
Thee reigning in the stead of Laius slain,
He clasped my hand and supplicated me
To send him to the alps and pastures, where
He might be farthest from the sight of Thebes.
And so I sent him.

The herdsman is in the "alps and pastures" somewhere, "farthest from the sight of Thebes," yet he appears just moments later to tell his story.

Regarding the "unity of place," the physical action of Oedipus Rex occurs in only one place: "in front of the palace at Thebes." Characters come and go from the palace, and the audience never sees them come from or go to anywhere else.

The imaginative action of Oedipus Rex—the action that takes place in the audience's mind—occurs in several locations far from and near to the palace at Thebes.

The audience imagines Creon going to and returning from the Oracle at Delphi, the baby Oedipus being taken into the mountains near Thebes to die, then being adopted by Polybus and Merope in Corinth, Oedipus meeting and killing Laius where three roads meet on his way to Thebes, Jocasta hanging herself in her rooms in the palace, and Oedipus finding her and poking out his eyes with the golden pins from her robe, and so on.

Unity of place isn't simply a theoretical limitation imposed on the ancient Greek tragedies. Even though Sophocles added the third actor to the performance of tragedies, there were still only three actors who had to portray all of the characters in the play, and the physical restrictions of the ancient Greek theaters simply didn't accommodate multiple changes in location. The actors, all three of them, couldn't go anywhere else.

The question of "unity of action" in Oedipus Rex raises one major issue.

The "action" of Oedipus Rex focuses primarily on "Who killed Laius?" However, at the same time that Oedipus and all the other characters are following the "Who killed Laius?" plotline, another issue arises—"Who is Oedipus?"

As the play progresses, the "Who killed Laius?" issue becomes secondary at times to the "Who is Oedipus?" inquiry. A considerable portion of the play is given over to this line of inquiry, even to the extent that the audience might forget that the main plot of the play—the "action" of the play, is supposed to be "Who killed Laius?"

Eventually the "Who is Oedipus?" issue is resolved, which, in turn, resolves the "Who killed Laius?" issue, but the question remains as to which of these represents the true "action" of the play and whether the action of the play is truly unified.

The three Unities in Greek drama, as described in Aristotle’s rules of poetry in The Poetics, are the Unities of Time, Place, and Action; here, the entire dramatic action of Oedipus takes place in a 24-hour period, since the exposition (the action before the start of the play), such as the confrontation of Oedipus and his father, the marriage to his mother Jocasta, etc., are all discussed as actions happening before the dramatic action begins, but are not acted out on stage.  The entire play takes place at the entrance to Oedipus’ mansion – there are no interior scenes or locations in other cities, etc. (remember, this was before proscenium arches, set changes -- except for perioktoi --, etc.), and the entire dramatic action is Oedipus’ dilemma – there are no subplots or minor character developments/ distractions. Whether Aristotle was prescribing rules or simply describing already existing plays (by Aeschylus, Euripides, etc.) , the Unities became the criteria for "correct" dramatic construction for tragedies until the Renaissance.