There has been some serious scholarly smack talk concerning Euripides's use of choruses. The main criticism is their lack of effect on the action of the play. The Chorus in Medea is a good example of this. This group of Corinthian women mostly just hangs out, bemoaning the terrible things that are going down. The only time we see them actually try and do something is at the beginning of the play when they attempt to lift Medea from her melancholy. They advise:
If your husband has gone to adore
A new bride in his bed, why, this
Has often happened before.
Do not harrow your soul. For Zeus
Will succor your cause. What use
To lessen your life with grief
For a lost lord? (25)
The Chorus's arguments have no effect on Medea. In fact, our crafty protagonist ends up pulling the Corinthian ladies to her side, by appealing to them as fellow women imprisoned in a world of men. By the time Medea's done with them, they're singing an ode of female revolution. The ladies intone:
Back to their fountains
the sacred rivers are falling;
The cosmos and all morality
turning to chaos.
The mind of a man is nothing but a fraud
One day the story will change:
then shall the glory
or women resound,
And reverence will come to the race of woman,
Reversing at last the sad reputation of ladies. (58)
For the rest of the play the Chorus does nothing to stop Medea's bloody deeds. Some point this out as sloppy plotting of Euripides's part. It's odd that these women stand idly by as Medea, a foreigner, plots to assassinate their royal family. Creon seems like a nice enough guy. Yeah, he banishes Medea, but she was going around threatening to assassinate him and his daughter. It even turns out that he's an old softy, when he allows Medea to stay another day for the sake of her sons. So why would the Chorus do nothing to stop the murder of their amiable ruler?
The only justification we can come up with for the Chorus's inactivity is that, like Medea, they are extremely dissatisfied with the treatment of women in their society. Their ode to female revolution supports this idea. Perhaps they represent the large number of women that are put upon, but don't have the will for revolt. They could be seen as living vicariously through Medea. Perhaps she serves as an outlet for their repressed rage. Of course, even the Chorus balks when Medea takes it as far as killing her own kids. The Corinthian women pray fervently for Zeus to stop her. Unfortunately, their prayers go unanswered, and once again they are unable to affect the action of the play.
Rather than using the Chorus to advance or complicate the plot, Euripides chooses to use them to expound upon his themes. This is true in many of his plays. In Medea they sing of the destructive power of love, the sorrows of exile, and the horror of Medea's murderous revenge. They also serve to release the tension between each episode. Euripides's unconventional use of the Chorus is yet another example how he challenged the dramatic status quo of his day. Over the course of his career they became less and less essential to his dramas. Some scholars theorize that, if he'd had his way, he would have fazed them out altogether, instead filling the plays with more of the realistic dialogue which he is so famous for inventing. In the Athenian dramatic competitions, however, this unconventional step would have been sacrilege.