Dramatic Irony in Macbeth

In order to ensure a truly cathartic reading experience of the Shakespearean tragedy, Macbeth, it is important to gain an understanding of several literary terms. The following post focuses on dramatic irony.
What is Dramatic Irony?
Dramatic irony is a literary device used in literature, particularly in plays, referring to the words or actions of a character that have a different meaning for the audience than they do for the character(s) in the play themselves. Often, the audience will recognize the significance of given phrase or action of a character because they have acquired additional knowledge surrounding the character and their future through other characters in the play prior to the event, while the character involved is ignorant of this.
The Roots
The characters’ ignorance, which is unintentional, ties in with irony’s roots. The word irony is derived from the Latin word ironia, which itself is derived from the Greek, å?ñùíåßá (eironeia) signifying ‘feigned ignorance’.
Dramatic irony, as a device, finds its roots in Sophocles’ famed work, "Oedipus". Oedipus, the king of Thebes, hears a prophecy from the Oracle of Delphi that he would kill his father and marry his mother. In order to prevent this, he leaves Thebes. On his journey, he meets a man at an intersection and they come into a dispute over who has the right of way. Oedipus, after being poked by the man’s goad, kills the man. He continues and after correctly answering the riddle of a Sphinx which was terrorizing Thebes, he is awarded the throne of Thebes and marries the previous king’s widow The dramatic irony about this is that through hints from minor characters, the reader knows that man he kills during the roadside dispute was his father, while the previous king’s wife is indeed his mother, thus fulfilling the prophecy. In the play, however, Oedipus is unaware of this.
Dramatic irony appears in the works of numerous other authors such as Aristophanes, Plautus, Goethe, Miles Gloriosus, Molière and Mark Twain, and is still widely used in a variety of media forms in our day and age.
Examples of Dramatic Irony in Macbeth
There are several examples of dramatic irony in Macbeth but there a few very prominent ones. In the first act, when the three witches reveal to the audience that Macbeth has been made Thane of Cawdor, he does not know this. During their meeting with him they inform him that he will become Thane. Macbeth shows disbelief in their proposition while the audience is aware that he has already been made Thane of Cawdor. A second example of dramatic irony is when Duncan is approaching Macbeth’s castle and he remarks how the castle has "a pleasant seat [and] the air nimbly and sweetly recommends itself unto [his] gentle senses" (1.6.1-3). The audience is aware that Duncan will most likely be killed shortly in that very castle that he finds so pleasant, displaying how a simple phrase has two meanings, one significance for the audience and another for the Duncan who is ignorant of Macbeth’s plots against him. Another example is in 2.3 where the porter jokes about being hell’s gatekeeper while talking to Macduff and Lennox. However, because he is drunk, they pay little attention and attach little worth to what he says. Ironically, the porter is guarding the chamber where Duncan lies murdered and the audience is aware of this, while the characters in the play are not.

Sources
Baker, Lyman A.. "Critical Concepts: Dramatic Irony." Kansas State University. 30 August 2000. 2 February 2007 <http://www.k-state.edu/english/baker/english320/cc-dramatic_irony.htm>.
Flanagan, Mark. "Dramatic Irony." About.com. 23 August 2006. 1 February 2007 <http://contemporarylit.about.com/cs/literaryterms/g/dramaticIrony.htm>.
"Oedipus." Wikipedia. 1 February 2007. 1 February 2007 <http://en.wikipedia.org/wiki/Oedipus>.
Thuleen, Nancy. "Dramatic Irony and Metadrama as a Vehicle for Social Criticism in the Works of Aristophanes, Plautus and Goethe." nthuleen.com. 5 May 1993. 1 February 2007 <http://www.nthuleen.com/papers/177paper.html>.
Toscan, Richard. "Dramatic Irony." Virginia Commonwealth University. N.d.. 1 February 2007 <http://www.vcu.edu/arts/playwriting/irony.html>.