What reason does Macbeth give for why Banquo should be killed in Macbeth?

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favoritethings eNotes educator| Certified Educator

In addition to feeling bitter as a result of Banquo's prophecy—that he would father kings—Macbeth resents Banquo's noble character.  He says,

Our fears in Banquo
Stick deep, and in his royalty of nature
Reigns that which would be feared. (3.1.51-53)

Macbeth claims that Banquo is wise and courageous without being reckless.  In short, Banquo conducts himself with honor, like Duncan or any good monarch would do.  Macbeth fears that Banquo's "royalty of nature" will pose a threat to him, and so it is one reason Macbeth has to order the murder of his former best friend.

Further, Macbeth is bitter as a result of the idea that he will not pass his crown on to his own children (he has none); that he, instead, has saddled his own conscience in order to secure the throne for the descendants of Banquo.  He says,

For Banquo’s issue have I filed my mind;
For them the gracious Duncan have I murdered;
Put rancors in the vessel of my peace
Only for them; and mine eternal jewel
Given to the common enemy of man,
To make them kings, the seed of Banquo kings! (3.1.67-74)
Macbeth is angry that he has destroyed his own peace to become king, and that everything he has done will be to make Banquo's children kings.  Therefore, he decides to kill Banquo and his only child, Fleance, so that he can prevent Banquo's line from ever taking the throne.  He fails, of course, and James II of England, the king on the throne of England at the time Macbeth was first performed, can actually trace his lineage back to both Duncan and Banquo!
litteacher8 eNotes educator| Certified Educator

Banquo has done nothing wrong, and does not deserve to be killed.  Yet Macbeth is suspicious of him.  He was there when Macbeth heard the prophecies.  One of the prophecies referred to Banquo’s heirs being heirs to the throne.  Macbeth is therefore concerned, and decides Banquo must die.

To be thus is nothing,

But to be safely thus. Our fears in Banquo

Stick deep, and in his royalty of nature

Reigns that which would be fear'd. ’ (Act 3, Scene 1)

Unlike the murder of Duncan, Macbeth has no qualms about killing Banquo.  Banquo is a good friend, and has never been disloyal to Macbeth.  Yet he is afraid of his old friend.  He worries that Banquo will be suspicious of Duncan’s murder, since he was there when Macbeth received the prophecy that he would be king.  He also wants to avoid a “fruitless crown,” so he decides to kill Banquo and his son Fleance in order to ensure that none of Banquo’s “issue” take the throne after him.

Macbeth’s lack of sympathy for Banquo demonstrates the denigration of his moral character.  When Banquo’s ghost appears, Macbeth’s reaction is not guilt but anger.  He is annoyed that Banquo’s ghost should taunt him by appearing from the grave when he is supposed to be out of the way.