What does Macbeth mean when he says "There's comfort yet, they are assailable. Then be thou jocund" in Macbeth?
In Act 3, Scene 2, Macbeth tells his wife:
O, full of scorpions is my mind, dear wife!
Thou know'st that Banquo and his Fleance lives.
She is equally concerned about this fact. She has expressed this torment to herself just before her husband enters.
Naught's had, all's spent,
Where our desire is got without content.
'Tis safer to be that which we destroy
Than by destruction dwell in doubtful joy.
She does not want Banquo to be sire of a whole line of Scottish kings any more than does her husband. She tells him:
But in them nature's copy's not eterne.
This seems to be the same as saying that if the father and his only son could be eliminated it would negate the witches prophecy. Here both Macbeth and his wife are conspiring against Fate itself. How could the witches' prophecies for Macbeth have come true without the prophecy concerning Banquo and his heirs also coming true? Macbeth believes it is possible because he wants to believe it. He tells his wife:
There's comfort yet; they are assailable.
Then be thou jocund.
Macbeth has already arranged to have Banquo and Fleance assaulted and murdered outside the castle when they return from their ride. All Macbeth and his wife have to do is to be "jocund," that is, cheerful and carefree, during the evening at the banquet until the bad news is brought to them. They will be surrounded by witnesses who will see that they were not involved in the killing.