Macbeth's mental deterioration begins when he kills King Duncan and continues as he gradually becomes a ruthless murderer, while Lady Macbeth's mental decline is the most conspicuous in Act 5 in the famous sleepwalking scene.
Firstly, let us focus on Macbeth's hallucinations. His ambition to murder Duncan so that he could become the king proves to have a very detrimental effect on him. Although he achieves his dream of becoming the ruler of Scotland, he loses his inner peace and stability for good. This is evident in the scenes when he appears to behold certain objects and apparitions, such as the invisible knife, the ghost of Banquo, etc. Here are some of the quotes that demonstrate Macbeth's descent into insanity:
Is this a dagger which I see before me,
The handle toward my hand? Come, let me clutch thee.
I have thee not, and yet I see thee still.
Art thou not, fatal vision, sensible
To feeling as to sight? or art thou but
A dagger of the mind, a false creation,
Proceeding from the...
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