The cause is the realization that his daughters Goneril and Regan do not love him. What finally pushed him over the edge was the cruel actions afflicted on him by the people that supposedly loved him.
To such a lowness but his unkind daughters. … 'Twas this flesh begot Those pelican daughters describes Lear of the cruelty of his daughters (III.iii.76,80-81).
The character of Lear produces the theme of madness by expressing his own increasing insanity and reasons the reason for it in raving tangents.
The style and depiction of the theme of madness are very different in both plays. Macbeth shows madness in the main characters with lots of imagery, giving a very physical sense of feeling towards the audience making them have a better understanding of what the characters are feeling. In King Lear madness is depicted through the main characters dialogue. This is meant to show the psychological turmoil going through the character’s mind which helps the audience understand why and what the character is doing within the play.
In conclusion it is clear that madness was a very re occurring theme in both plays King Lear and Macbeth. However, the style in which the madness was depicted in each play is very different, in Macbeth madness within the main characters is shown through basic hallucinations through sight and smell, whereas in King