Shakespeare establishes the core tensions between Lear and his daughters right at the beginning of the play, as he challenges them to make elaborate declarations of their love for him in Act 1, Scene 1. Goneril’s speech is particularly over-the-top:
Sir, I love you more than words can wield the matter,
Dearer than eyesight, space, and liberty,
Beyond what can be valued, rich or rare,
No less than life, with grace, health, beauty, honor;
As much as child e'er loved or father found;
A love that makes breath poor and speech unable.
Beyond all manner of so much I love you.
Goneril's speech is rife with hyperbole meant to drive home just how deeply she supposedly cares for Lear. She clearly states that she loves him "more than words can wield the matter," which is obviously untrue, considering the fact that she's currently speaking and thus using words. Her overstatement continues in the subsequent lines, as she insists that she loves him more than anything that "can be valued." To that end, she asserts that she loves Lear quite a bit more than life itself. Finally, she returns to her first hyperbolic statement about loving her father "more than words can wield the matter," this time saying that her love "makes breath poor and speech unable"—yet another hyperbolic and clearly contradictory statement, considering that she's literally in the middle of speaking.
Although the ending of King Lear stings the audience with the lasting power of Lear’s grief, he spends most of the play more angry—and, eventually, insane—than sad. In Act 1, Scene 4, he focuses his rage on his treacherous daughter, Goneril:
If she must teem,
Create her child of spleen, that it may live
And be a thwart disnatured torment to her.
Let it stamp wrinkles in her brow of youth,
With cadent tears fret channels in her cheeks,
Turn all her mother’s pains and benefits
To laughter and contempt, that she may feel
How sharper than a serpent’s tooth it is
To have a thankless child.— Away, away!
Lear uses hyperbole and metaphor on several occasions in this passage to properly convey the scale of his anger. He wishes that Goneril will bear a child so spiteful that her tears carve channels into her very cheeks, as if her cheeks are stone and her tears some sort of corrosive acid. Then, Lear expresses his wish that Goneril will learn how having such a spiteful child is “sharper” than even the bite of a serpent. This is a metaphorical comparison between the emotional pain of betrayal and the physical pain of a terrible snake bite, and it rests in the hyperbolic assertion that such a betrayal is every bit as agonizing as a mortal wound. Hyperbole allows Shakespeare to convey the proper severity of his characters’ emotions without needing to be constrained by the bounds of reason, and Lear's disgust is clearly displayed by the bitter cruelty of his remarks against Goneril.
When Gloucester makes his final stand against Regan and admits that he has sent Lear to Dover, he explains his reasoning for his defiance in no uncertain terms, using hyperbole to emphasize his point:
Because I would not see thy cruel nails
Pluck out his poor old eyes, nor thy fierce sister
In his anointed flesh stick boarish fangs.
The sea, with such a storm as his bare head
In hell-black night endured, would have buoyed up,
And quenched the stellèd fires;
Yet, poor old heart, he holp the heavens to rain.
If wolves had at thy gate howled that stern time,
Thou shouldst have said “Good porter, turn the key.”
All cruels else subscribe. But I shall see
The wingèd vengeance overtake such children.
This passage presents a wealth of literary devices, including two striking uses of hyperbole to describe the storm and Regan’s depravity. The storm that stranded Lear was so violent, Gloucester asserts, that had it been over the ocean the waves would have put out the very fires of the stars. In the midst of this storm, however, Regan refused to yield and admit her father to the castle, even though the storm was so dramatic that she would have admitted a pack of wolves had they howled at the gates. While no storm could produce waves that high, and while Regan is unlikely to take pity on a pack of wolves, the effect of these hyperbolic statements is to heighten the drama of the moment. This is a fitting escalation, given that this is something of a climactic speech for Gloucester; immediately after he finishes speaking, Cornwall will punish him for his insolence by gouging out his eyes. By leading Gloucester’s rage above and beyond the bounds of reality, Shakespeare raises the intensity of the language to match the intensity of the action.