Compare King Lear's mental states and his relationship with his daughters in Act 1 Scene1, Act 2 Scene 4, and Act 4 Scene 6.

In the opening scene of Shakespeare's King Lear, Lear seems somewhat indifferent to his daughters, Goneril, Regan, and Cordelia. He says that he intends to divide his country in three parts and bestow a part on each of his daughters.

LEAR. Know that we have divided
In three our kingdom: and 'tis our fast intent
To shake all cares and business from our age;
Conferring them on younger strengths, while we
Unburthened crawl toward death. (1.1.36–40)

Lear isn't doing this to show his love for his daughters, but to avoid conflict between and among them after he dies.

LEAR. We have this hour a constant will to publish
Our daughters' several dowers, that future strife
May be prevented now. (1.1.42–44)

This seems like a reasonable, rational, and politically expedient thing to do. The only issue is which of his daughters gets which part of his kingdom, and that depends on each of their answers to his question, "Which of you shall we say doth love us most?" (1.1.49).

Goneril and Regan respond in what Lear considers an appropriately loving manner towards him, but Cordelia, unable to faun over her father and flatter him like her sisters, answers Lear in a simple and straightforward manner.

CORDELIA: ... I cannot heave
My heart into my mouth: I love your majesty
According to my bond; nor more nor less ... (1.1. 95–97)

Lear is displeased with her response. He disinherits her, calls her his "sometime daughter" (1.1.126), banishes her, and sends her away with nothing. This is the same daughter whom just moments ago he called "our joy" (1.1.86) and of whom he said, "I loved her most" (1.1.130).

However politically astute Lear might appear, he's nevertheless ruled by his emotions and his immense ego.

In act 2, scene 4, Lear meets with Regan, and he complains to her bitterly about his treatment by Goneril, who has given Lear an ultimatum that if he wishes to stay with her, he must give up half his retinue of one hundred knights and soldiers.

To Lear's surprise and dismay, Regan sides with Goneril. She tells Lear to go back to Goneril, which Lear refuses to do. Then she offers Lear an ultimatum of her own. If he intends to stay with her, he must reduce his retinue to "but five and twenty" (2.4.267).

While Lear is recovering from that shock, Goneril strikes at him again.

GONERIL. Hear me, my lord;
What need you five and twenty, ten, or five,
To follow in a house where twice so many
Have a command to tend you? (2.4.281–284)

Regan offers the last word on the matter.

REGAN. What need one? (2.4.285)

Lear is outraged by this and utterly disbelieving of what his daughters have done. He rages impotently at them.

LEAR. ... I will have such revenges on you both,
That all the world shall—I will do such things,—
What they are, yet I know not: but they shall be
The terrors of the earth. (2.4.301–304)

Lear's fragile mental state is deteriorating, and he's barely able to control his emotions.

LEAR. You think I'll weep
No, I'll not weep:
I have full cause of weeping; but this heart
Shall break into a hundred thousand flaws,
Or ere I'll weep. O fool, I shall go mad! (2.4.304–308)

In a rage, Lear leaves Regan and Goneril and goes out into a raging storm with only his Fool and loyal Kent to keep him company.

By act 4, scene 6, Lear's grasp of reality is tenuous at best. He thinks that blind Gloucester is Goneril with a white beard, and it's difficult to know if he joking or mad. A short time later, Lear recognizes Gloucester for who he is, and Gloucester recognizes Lear's voice.

GLOUCESTER.The trick of that voice I do well remember:
Is 't not the king?

KING LEAR. Ay, every inch a king:
When I do stare, see how the subject quakes ... (4.6.120–123)

A gentlemen and attendants sent by Cordelia to rescue Lear enter the scene, but Lear runs off, fearing that Goneril or Regan sent them to take him prisoner.

Gloucester says what everyone knows by now to be true:

GLOUCESTER. The king is mad ... (4.6.301)

In time, Goneril and Regan turn on each other. Goneril poisons Regan, then kills herself. Lear reconciles with Cordelia, but before they can fully restore their relationship, Cordelia is executed on Edmund's order after her forces are defeated in battle, and Lear dies of grief because of her death.

Analyze King Lear's mental condition from Act 1, Scene 4 to Act 3, Scene 4.

Some critics believe that Lear in mad as the play begins.  Why else would he divide up his kingdom?  Why else would he wrest authority away, to his children?  Why else would he devise a silly love contest in his kingdom's allotment?  If not mad, these acts are certainly foolish.

His age doesn't help.  Lear is old for that time.  Senility and dementia are common for anyone that age, not to mention the added pressure of being King.  Stress can ravage a body.

We certainly have a correlation here: a divided kingdom equals a divided mind.  Any king who divides his kingdom is asking for problems, suffering, and unruliness.  Worse, any father who divides his love between his children is setting himself and them up to fail.  And any father or king who enacts a contest to determine awards is certainly asking for the worst in human behavior.  Greed and ingratitude soon rear their ugly heads.

Casting away a child (Cordelia) and a trusted advisor (Kent) will cause a detachment from reality.  Compound this with two selfish forces (Regan and Goneril) competing for land and Lear serves up a recipe for mental anguish.  Critic Laurence Stern wrote:

Nobody, but he who has felt it, can conceive what a plaguing thing it is to have a man's mind torn asunder by two projects of equal strength, both obstinately pulling in a contrary direction at the same time.

So it is with Lear.  Love and competition for love tear his mind into madness.  He cannot reconcile the two.  His madness is a retreat from reality, a kind of denial of reality.  He cannot accept the fear that his daughters and subjects do no love him.  He fears they may only want from him.

R. Moore, in his essay "Madness in King Lear," says:

Several things attribute to Lear's eventual madness. The Fool, initially, plays a large part in pointing out to the King his foolish mistakes. Even before the onset of Lear's madness, the Fool is anticipating it:

thou hast pared thy wit o'both sides, and left nothing i' the middle.
(I.iv.194-95)

Lear's gradual realization of the disloyalty of his two elder daughters also leads him to anticipate his oncoming madness. Reproaching himself for his blindness, he says of himself, "Either his notion weakens, his discernings/ Are lethargied," (I.iv.236-37) and later, ". . . let thy folly in,/ And thy dear judgement out!" (I.iv.280-81) It is Lear's reaction to Goneril's refusal to house him together with his whole retinue that marks the first real premonition of his madness, and the Fool suggests that it is his lack of wisdom, which accompanied his old age, that will be the cause of it.