In Shakespeare's Hamlet, to what source does the Queen attribute Hamlet's madness?Act 3 scene 1
As noted in the first answer to your question above, Queen Gertrude hopes that the cause of her son's apparent madness may be his love for Ophelia. In Act 3, Scene 1, she says:
And for your part, Ophelia, I do wish
That your good beauties be the happy cause
Of Hamlet's wildness. So shall I hope your virtues
Will bring him to his wonted way again,
To both your honors.
However, in Act 2, Scene 2, when Polonius tells Claudius and Gertrude, "...I have found / the very cause of Hamlet's lunacy," Gertrude says to her husband:
I doubt it is no other but the main,
His father's death, and our o'erhasty marriage.
Evidently, Polonius' long explanation of his diagnosis of Hamlet's lunacy as being the result of his thwarted passion for Ophelia has some influence on Gertrude's thinking. When Claudius asks her, "Do you think 'tis this?" she replies, "It may be, very like."
So the Queen evidently would like to think that she is not responsible for her son's apparent madness, although she may still secretly fear that she is at least partly responsible.
In William Shakespeare’s Hamlet, Act III, Scene I, Rosencrantz and Guildenstern have reported that Hamlet appears wild and distracted and will not reveal the cause of the disturbance. Queen Gertrude, who is Hamlet’s mother, speculates that the cause of this disturbance may be that he is in love with Ophelia, daughter of Polonius. This would be a very unequal match for a Prince of Denmark. The Queen then enlists Ophelia’s aid in helping discern Hamlet’s mental state. Of course, Hamlet is not actually mad, but feigning madness as part of his revenge plot. Hamlet continues this pretense in his conversation with Ophelia, leading to her actual madness and suicide.