Explain the plot construction of Othello.
There are different approaches to analyzing plot structure in drama, and, indeed, different approaches to structuring a drama. Othello follows a five-act plot structure which broadly adheres to the so-called Classical dramatic structure as described by Aristotle in his Poetics. The story first presents its complication—which is driven by a fatal flaw, or hamartia, in the play's protagonist—rises to a climax, and then proceeds to unravel or resolve the complication.
Freytag divides dramas into five parts: the exposition, rising action, climax, falling action, and denouement. While Freytag's analysis was generally drawn from plays with five acts, Shakespearean plays with fewer acts can usually also be broken down according to these guidelines. In Othello, however, each act is generally (although not entirely) well matched to each part of Freytag's pyramid.
The exposition is contained to the first act, wherein we learn that Iago hates Othello, ostensibly because Othello promoted Cassio over Iago. Next, we learn that Othello has married Desdemona, and Othello makes his case to the Duke of Venice for having won Desdemona fairly. We also find out in the exposition of the play that Roderigo loves Desdemona, and can understand how Iago might use this in his plan.
The rising action of the play, then, comprises Act II and much of Act III, as we watch Iago ruin Cassio's reputation in Cyprus, sowing the idea in Othello's mind that he may not be a good officer after all. Iago then convinces Desdemona to try to restore Cassio's reputation with Othello. By chance, Emilia delivers to Iago the handkerchief with which he can embark upon the next stage of his plan, polluting Othello's mind; the third scene of this act, when we watch Iago convince Othello of Desdemona's treachery, is the play's climax.
The distinction between the falling action and the denouement can be more difficult to pinpoint. Act IV of this play is certainly entirely falling action, as Othello begins to punish Desdemona for the deeds Iago has convinced him she has committed; arguably, everything up to the point at which Othello strangles Desdemona is falling action. After this, from the point at which Emilia explains to Othello what has happened and reveals what Iago has done, the denouement—or final unraveling of the plot—takes us to the end of the play, with all major cast members but Cassio and Iago dead.
Othello has a plot based on deception. It is based around the scheming of Iago. Iago hates Othello and so with the help of Rodrigo awakes Desdemona's father. Desdemona having just run away with Othello. Starting there, the rest of the plot continues the same way, with Iago convincing others (as he did Roderigo) or perceived threats or slights that are not actually there. Iago decides to implicate Cassio in an affair with Desdemona, to ruin Othello's life. Iago sets it up, so that Othello begins to suspect Desdemona (he finds her handkerchief in Cassio's possesion, for example). Othello, convinced by Iago of Desdemona's guilt, decides to kill her. Iago convinces Rodrigo to kill Cassio (although Iago ends up killing Cassio himself), Othello kills Desdemona, learns that he has been wrong about her affair, and kills himself, not before trying to kill Iago, who is led off alive.
As you can see, the plot is constructed through a series of deceptions, all created by Iago.
It is also important to address the structure of the play in answering this question. Iago's soliloquys shape the entire play. If not for his soliloquys, we would not understand how his scheme is planned, how he contradicts himself each time he reveals his motives, why his ego is hurt at points during the play, and i the end, each soliloquy adeptly forwards the plot. For the audience, without the knowledge of Iago's plans, we would not entirely understand his power over Othello, or for that matter, any character in the play. The structure of the play, therefore, mirrors Iago's control.