O spirit of love, how swift and lively are you,
That despite your vastness
Which absorbs like the sea, nothing enters,
Regardless of its worth and stature,
But quickly loses value and diminishes
In mere moments.

Orsino's initial reflection in Act 1, Scene 1, on his unreturned love for Olivia includes some of the most renowned lines and imagery in Shakespeare's entire body of work. These lines also highlight the key themes and issues in Twelfth Night.

The references to love and the sea in the aforementioned lines echo throughout the play's narrative. Orsino likens the vastness of love to the ocean’s boundless and overwhelming nature. (This is also mirrored in Juliet's words in Romeo and Juliet, Act 2, Scene 1: “My bounty is as boundless as the sea, / my love as deep. The more I give to thee / the more I have for both are infinite.”) He further explains that love can be destructive; just as the sea can engulf and degrade everything that falls into it, love can completely consume a person's mind and heart, leading to their ruin.

So full of shapes is fancy
That it alone is high fantastical.

These lines convey that love can manifest in various forms and is often highly imaginative. The term fancy frequently appears in Shakespeare's works in relation to love, especially love that is deceptive or illusory. Orsino's overly romanticized affection for Olivia is an example of such fancy; he loves with his eyes and only imagines that his love stems from the heart. This notion of fanciful, illusory love sets the stage for Orsino's journey in the play. He must overcome his imaginative fancies about love to understand what true love genuinely is.

O when mine eyes did see Olivia first,
Methought she purged the air of pestilence.

Orsino’s proclamation of love for Olivia sets the stage for the play’s exploration of love's multifaceted nature. In Illyria, love manifests in various forms: love at first sight, the contrast between love and lust, self-love, indulgent love, the love found in true friendship, and genuine true love. This particular quote reveals that Orsino’s affection for Olivia stems from his initial sighting of her; his love is about visual attraction rather than emotional connection. His words also equate love with disease, specifically a pestilence or plague. For the Elizabethans, the term pestilence evoked negative and terrifying connotations since the plague was a constant threat. Orsino implies that merely seeing Olivia can purify the air around her, but the irony is that he himself has succumbed to the disease of love.

That instant was I turned into a hart,
And my desires, like fell and cruel hounds,
E’er since pursue me.

This passage is one of the play’s numerous classical references, portraying love through violent imagery. Orsino vividly expresses his unfulfilled love for Olivia by likening himself to the hunter Actaeon. In Greek mythology, Actaeon accidentally saw the goddess Artemis bathing, and as a punishment, she transformed him into a stag, leading to his being hunted and torn apart by his own dogs. These lines underscore the destructive potential of love, especially illusory love. Orsino also continues the hart/heart pun from Valentine’s earlier inquiry about whether Orsino plans to hunt that day.

And what should I do in Illyria?
My brother, he is in Elysium.

In Act 1, Scene 2, Viola believes her brother has drowned in the storm that sank their ship. She questions what she should do now that her brother is no longer alive to protect her. Elysium, the Greek equivalent of heaven, symbolizes a place of peace and eternal joy. The phonetic similarity between Illyria and Elysium suggests a connection, implying that Illyria will ultimately become a place of safety and happiness for Viola, providing the healing she needs after the (seeming) loss of her brother.

There is a fair behaviour in thee, captain
And though that nature with a beauteous wall
Doth oft close in pollution, yet of thee
I well believe thou hast a mind that suits
With this thy fair and outward character.

Viola shares her plan to disguise herself as a boy with the sea captain who rescued her from the storm. She remarks that while a pleasant and kind appearance can sometimes hide a corrupt soul, she believes the captain's nature is as genuine and loyal as his looks suggest. Because of this, she decides to trust him with her secret plan to dress as a boy for her protection in Illyria and even seeks his assistance in accomplishing this.

Even so quickly may one catch the plague?
Methinks I feel this youth’s perfections
With an invisible and subtle stealth
To creep in at mine eyes.

Similar to Orsino in act 1, scene 1, Olivia acknowledges the concept of love at first sight in scene 5. She proclaims that “Cesario’s” charms are affecting her deeply, and she is overwhelmed by what she has witnessed. Just as Orsino’s affection for Olivia is portrayed as “fancy” or illusory love, so is Olivia’s sudden and intense emotion towards Viola-Cesario. This also serves as a comedic moment because, as the audience, we are aware of her vow to mourn for seven years (as reported by Valentine in act 1, scene 1). With the arrival of Viola-Cesario, Olivia’s solemn promise to honor her brother's memory is completely upended by her extravagant reactions to this charming young man. This is the point where Olivia’s character reveals the comedic edge that persists throughout the play, transforming her image from the romantic, tragic figure in mourning described by Orsino.

Fate, show thy force; ourselves we do not owe.
What is decreed must be; and be this so.

Olivia’s enthusiastic rhyming couplet after Viola-Cesario’s departure at the end of act 1, scene 5, highlights another theme of the play: Fate as the ultimate ruler of human destiny. Olivia’s words are akin to Viola’s plea to Time to “untangle this, not I,” when she realizes that Olivia “loves me sure.” In this scene, Olivia entrusts the situation to Fate, arguing that humans do not control their destinies; hence, she will wait to see what unfolds. (See also Helena in All’s Well That Ends Well, whose perspective in act 1, scene 1, is the opposite: “Our remedies oft in ourselves do lie / Which we ascribe to heaven. The fated sky / Gives us free scope.”) She concludes with a variation on the saying “What must be will be.” This joyful resolution to let Fate take its course foreshadows the comedic scenario at the play’s end where Olivia attempts to take control of Fate by marrying “Cesario.”

Did you never see the picture of “we three”?

This question from Act 2, Scene 3, refers to contemporary seventeenth-century "trick" pictures of two fools or clowns, where the viewer becomes the third "fool." An anonymous painting titled Wee Three Logerhds possibly depicts the famous jesters Tom Derry and Archie Armstrong. Shakespeare may have had a similar painting in mind when he wrote this line. Other versions of these images existed as inn signs, showing the two "fools" as donkeys, which could explain Sir Toby's greeting to Feste in Act 2, Scene 3: "Welcome, ass."

Dost thou think that because thou art virtuous there shall be no more cakes and ale?

Sir Toby is confronting an angry Malvolio, who has come to check on the noise from the midnight revelry of Sir Toby, Sir Andrew, and Feste. The "cakes and ale" in Sir Toby's speech symbolize the play's title and portray Illyria as a place of ongoing informality and celebration. Twelfth Night marked the end of the Christmas season, a period of Yuletide leniency in English households over twelve days. During this time, regular conventions were ignored, focusing solely on merrymaking and festivity.

Malvolio, described as "a kind of puritan" in Act 2, Scene 3, embodies the puritanical disapproval of excess eating and drinking, so much so that he is ready to challenge his employer's uncle about his behavior. Sir Toby's mocking question challenges both Malvolio's authority and his puritan beliefs. It underscores Toby's contempt for his niece's steward and foreshadows the "revenge" he exacts on Malvolio later in the play by imprisoning him in the dark house.

Why, thou hast put him in such a dream that when the image of it leaves him, he must run mad.

The theme of love teetering between dreams and madness is vividly portrayed in act 2, scene 5 of the play. Maria comments on the "dream" Malvolio experiences, believing Olivia loves him due to the prank orchestrated by Sir Toby, Sir Andrew, and Fabian. She implies that once Malvolio discovers the truth, he will be driven to madness. This can be contrasted with Sebastian's lines in act 4, scene 1, and his soliloquy at the start of act 4, scene 3. Olivia professes her love to Sebastian, who has never met her before. In act 4, scene 1, he initially thinks, "this is a dream. . . . If it be thus to dream, still let me sleep." The dreamlike state persists, and by act 4, scene 3, Sebastian is frantically searching for an explanation for his predicament. He tries to reassure himself that "’tis not madness" and that "this may be some error but no madness," but ultimately concludes, "I am mad, / Or else the lady’s mad." Unlike Malvolio, Sebastian's "dream" is fleeting; the apparent madness ends when the twins' identities are unveiled, allowing him to marry Olivia. However, Malvolio’s ordeal in the dark house transforms his "dream" into a living nightmare, where his claims of sanity are dismissed, leading to his humiliation and degradation.

Have you not set mine honour at the stake
And baited it with all th’unmuzzled thoughts
That tyrannous heart can think?

In act 3, scene 1, another instance of love's intense violence is depicted. Olivia refers to the Elizabethan sport of bear-baiting, where a bear is tied to a stake and attacked by dogs until it is torn apart. Her metaphor suggests she is the bear, and her love for Cesario is akin to the unmuzzled dogs savagely tearing at the bear's flesh. This violent imagery mirrors Orsino's comparison at the play's beginning, where he likens himself to Actaeon being devoured by dogs.

Come, we’ll have him in a dark room and bound. My niece is already in the belief that he’s mad.

Sir Toby’s command in Act 3, Scene 4, continues the theme of madness but unveils a darker and more disturbing aspect of the play. While love can bring about a kind of madness, leading to the melancholy experienced by Orsino, Sir Toby refers here to genuine mental insanity. During this period, the common treatment for insanity was to confine the patient in a dark room, believing that the darkness would expel evil spirits from the patient’s body. This harsh and often violent practice persisted for many years. Sir Toby’s suggestion to subject Malvolio to this "cure," despite knowing that Malvolio is not truly mad, reveals a sinister side to Sir Toby’s personality. (See also Dr. Pinch’s proposed treatment for Antipholus and Dromio of Ephesus in Act 4, Scene 4, of The Comedy of Errors: “They must be bound and laid in some dark room.”)

Nothing that is so, is so.

This line from Act 4, Scene 1, perhaps more than any other, encapsulates one of the dominant themes of Twelfth Night: the theme of deceptive appearances. In the world of the play, almost everything is an illusion: appearances, love, even death. Feste speaks this line to Sebastian, whom he mistakes for Cesario. However, Cesario is not who he appears to be either. The play revolves around a man who seems to be in love with a woman who does not reciprocate his feelings, and this woman is in love with another woman who appears to be a man. Viola’s brother seems to have drowned, and Sebastian believes his sister perished in the shipwreck. These images of deceptive reality also capture the mercurial spirit of Illyria.

Shakespeare has imbued Illyria with a magical quality that allows for these inversions of normal behavior and situations. It is only in Illyria that the festival of Twelfth Night can be perpetually celebrated by Sir Toby and his companions; only in Illyria where girls can disguise themselves as boys; only in Illyria where seemingly dead siblings can be resurrected. Illyria appears to be a real place with a coastline, storms, and ruling dukes, but it too is not what it seems. It is a fantastical world of illusion and fantasy, comparable to Shakespeare’s other enchanted worlds: the Forest of Arden in As You Like It and Ephesus in The Comedy of Errors.

Clown: But do you remember—“Madam, why laugh you at such a barren rascal, and you smile not, he’s gagged”? And thus the whirligig of time brings in his revenges.

Malvolio: I’ll be revenged on the whole pack of you!

In Act 5, Scene 1, Feste’s lines bring Malvolio back to the moment in Act 1, Scene 5, when he dismisses Feste's wit. It’s evident that Feste has harbored resentment towards Malvolio for his condescending rebuke, and the prank in the dark house was Feste’s way of getting revenge. The phrase “whirligig of time” serves to explain why Malvolio has been treated as he has. The wheel has turned, and Feste’s comment suggests that with the Sir Topas prank, he and Malvolio are now even, and their “feud” can end. However, Malvolio doesn’t see it this way and seems determined to continue the conflict, which casts a shadow of reality over the play’s closing moments.

On stage, these lines have been interpreted in various ways, especially concerning Malvolio’s final line and exit. Malvolio’s threat could be aimed directly at those who orchestrated the “joke”—Maria, Sir Toby, and Fabian—or more pointedly at Feste, with whom he has ongoing animosity. In Act 2, Scene 3, Maria describes Malvolio as a “kind of puritan,” and it has been suggested that this line foreshadows the Puritan rule in England forty years later, during which theaters were closed and Twelfth Night celebrations ended.