Dialogue in Shakespeare's plays, as in most plays, is used largely to convey information to the audience. The author can become tedious if he has a character explain something to another character which the audience already knows. If Macbeth told his wife about his plans to have Banquo and Fleance ...
Dialogue in Shakespeare's plays, as in most plays, is used largely to convey information to the audience. The author can become tedious if he has a character explain something to another character which the audience already knows. If Macbeth told his wife about his plans to have Banquo and Fleance killed, he would be telling her everything that Shakespeare has taken great pains to convey to his audience in Macbeth's soliloquies and through his dialogue with the murderers. The audience does not know exactly how these murders are supposed to be executed, but that will be clearly shown in Act III.3 when it happens. If Macbeth told his wife all about it in advance, there would be a lot of unnecessary dialogue between them, and it would detract from the emotional effect of Act III.3, where the audience sees Banquo ambushed and killed while Fleance manages to escape. So Shakespeare has Macbeth tell his wife in Act III.2, when she asks,
What's to be done?
Be innocent of the knowledge, dearest chuck,
Till thou applaud the deed.
Macbeth is supposedly protecting his wife from being an accessory before the fact. But the real reason that he doesn't tell her "what's to be done" is that there is no need to communicate anything in dialogue to the audience. They already know he plans to have Banquo and Fleance killed, and they will soon find out how the murderers intend to do it.
Another interesting and apposite example of how Shakespeare avoids unnecessary dialogue can be seen in Julius Caesar. In Act II.1, Brutus finally yields to Portia's insistent pleading and says he will tell her everything she wants to know.
Hark, hark, one knocks.Portia, go in awhile,
And by and by thy bosom shall partake
The secrets of my heart.
All my engagements I will construe to thee,
All the charactery of my sad brows.
Leave me with haste.
Yet in Act III.4, it is evident that Portia now knows that Brutus is planning to lead an assassination attempt against Julius Caesar that day, and there has been no word of dialogue in the interim in which Brutus has explained this to his wife. The audience understands that Brutus has done as he promised and that Portia is now fully informed and has become, in effect, a co-conspirator.