In William Shakespeare's Othello, illusion too often disguises reality.  The themes of the play are riddled with illusions, for example, love and relationships, peoples personalities, schemes, friendship, and happiness.  All these aspects of the play are full of illusion, perhaps having only one "real" part to it, and that is the character of Emilia.
    Love and relationships are the greatest illusion in Othello.  The greatest of these being the relationship between Othello and Desdemona.  Throughout the entire play, Othello is declaring "I love the gentle Desdemona,"  but it seems this love is nothing but an illusion to hide the reality of their situation.  After always declaring his love for Desdemona, Othello's tune abruptly changes, when he begins to hate her, and even plots to kill her.  Othello states, "I will chop her into messes."  It almost starts to seem as if Othello and Desdemona's "love" is based purely on lust, as even when Othello hates Desdemona he still finds himself attracted to her.  His jealousy is sexual jealousy, not because he thinks Desdemona has fallen out of love with him.  Desdemona however lover the Moor to the end, even blaming herself for her own death, rather than letting Othello be blamed.  In this way her death was in vain, because all through the play she fights to keep a love alive that was nothing but an illusion.  Iago and Emilia's relationship however is more "real" than that of Othello and Desdemona.  They have not love, but only lust, however they do not pretend, or try to create an illusion that there is anything there that isn't.  Emilia and Iago are constantly fighting, and it is very clear to the audience how they feel about eachother.  With Othello and Desdemona however it is not so straight forward.   Othello creates for Desdemona and illusionary stat of comfort.  Desdemona is forced to live with the illusion that Othello still loves her.  Not so with Emilia and Iago.  Emilia is very well aware that Iago does not love her, and so she lives in a harsh reality.  Bianca and Cassio's relationship is also illusionary.  Bianca believes that Cassio will marry her, and Cassio lets her live this illusion.  When he and Iago are talking about her, Iago says, "She gives it out that you shall marry her / Do you intend it?"  To this Cassio does nothing but laugh, and then follows it up with laughing denials.  Bianca is living in a illusionary hope that Cassio loves her, just as Desdemona lives in an illusionary hope that Othello still loves her.  Emilia and Iago's relationship is the only "real" relationship in the play.  In this way illusion often disguises reality.
    Personalities in Othello are also often illusionary.  Iago is perhaps the most perfect example of this.  HE is absolutely two faced, and never says what he actually thinks.  Roderigo sums up Iago's entire personality to perfection.  "Faith I have heard too much;  for you words and performances are no kin together."  We, the audience are able to see through the illusion that Iago has built up for himself, but we are able to see what goes on in his mind.  HE is seen by most characters as an "honest" man, and is too aften described as "honest Iago."  Even Cassio says "I never knew a Flosrentine more kind and honest."  However, the audience knows that Iago is anything but hinest, but the characters are not able to see past this illusion.  Iago himself says "Men should be what they seem"  and later says "I amd not what I am."  Sometimes it seems almost like Iago can not see through his own illusion.  He even, appropriately swears "By Janus" the two faced Roman God.  Othello's personality is also full of illusions.  He shows a strength to the other characters that he does not in fact possess.  What strong man would so "easily be lead by th'nose"  as Iago so eloquently puts it.  Even Desdemona has little illusions in her personality.  Not in her loyalty to Othello, that is real enough, but in her loyalty to her father.  Lodovico describes her as a "Truly obedient Lady" whereas Brabantio says "O she has deceived me past thought," and goes on to say to Othello, "Look to her, Moor, if thou hast eyes to see. / She has deceived her father, and may thee."  Once again, Emilia is the only "real" character.  She always states things as they are, and how she feels about them, without glossing things over as many of the other characters do.
    The schemes in Othello are in themselves nothing but illusions.  Iago tries to create an issusionary world for Othello, which makes him see Desdemona as unfaithful, Cassi as a betrayer, and Iago as his closest friend.  Noe of these things are as they seem, but this is how Iago has schemed that Othello will see the world.  He is scheming from the beginning saying, "I follow him to serve my turn upon him," so Iago shows that Moor that he is loyal, but in reality is not.  His actual plan is to "Put the Moor...into a jealousy so strong that judgement cannot cure."  Othello's jealousy is real enough, but what it is based on, is nothing but an illusion.  Iago himself lives in this kind of jealous illusion, because his jealousy is based on events that never happened.  Iago want to "be evened with him, wife for wife," but has no reason to be, as Othello is innocent of the crime of adultery, just as Desdemona is.  So he says, "I'll set down the pegs that make this music," and so he does, and creates for Othello a world of illusion that disguises reality.
    Friendship in Othello is an illusion of epic scale.  Othello believes that Iago is his friend, but in reality he "hate[s] the Moor."  Iago even confesses that he wishes Othello to think they are friends.  "Make the Morr thank me, love me, and reward me / for making him egregriously an ass."  Iago actually want to use Othello, but all through the play Othello believes the illusion that "honest Iago" is his friend.  Iago and Cassio's friendship is also illusionary.  it is always part of Iago's plan to frame Cassio for having an affair with Desdemona, but he says, feigning friendship, "I had rather had my tongue cut from my mouth / Than do offence to Michael Cassio," and goes on to say, "Cassio's my worthy friend."  In reality Iago hates Cassio as much as Othello, because he received the promotion that Iago was meant to get.  Once more, Desdemona and Emelia's friendship is more reality than illusion.  Ath the end of the play Emilia chooses to defend her dead friend rather than her husband, and all through the play Emilia and Desdemona are confiding with eachother.  Illusion in friendship too often disguises reality, and it is good to see that there is at least on friendship in Othello which has escaped the tain ot illusion.
    Happiness is also an illusion is Shakespeare's Othello.  The characters are always feigning happiness, when in fact they are miserable.  Desdemona says in an Aside, "I am not merry, but I do beguile / The thing I am by  seeming otherwise."  Most of Othello's characters do this.  Pretend to be happy, but are in fact not.  From outward appearances anyone would think that Deasdemona and Othello had a perfect, happy marriage, but they cloaked their unhappiness in illusion so that no one could see the truth until it was too late.  Iago is always having to pretend to be happy to keep up his "honest" illusion, when inside he is really as sour as a lemon.  Once again Emelia is the only "real" character.  Although she is utterly miserable, she doesn't pretend to be happy for the sake of an illusion, as Desdemona does.  The only time Desdemona's unhappiness shows through is when she is alone, with Emelia, or right at the end of the play, when she knows her fate.  The only time she ever really shows her unhappiness to anyone else, is when she cries in front of Iago.  He says "Do not weep, do not weep.  Alas the day!"  This is just after Othello has called Desdemona a whore.  Almost everyone in Shakespeare's Othello has illusionary happiness disguising the reality of misery.
    In Othello illusion very often disguises reality.  Perhaps this is the real source of tragedy of Othello.