Shakespeare is well-known for using blank verse -in iambic pentameter, being lines that follow a "de dum,de dum rhythm- but also prose and even rhyme in establishing his characters. Macbeth explores various options in establishing a rhythm and Shakespeare is a master at creating drama, passion and revealing his characters' personalities through the use of poetry:
paying attention to characters who suddenly break into rhymed verse, or who slip into prose after speaking in blank verse, will heighten your awareness of a character’s mood and personal development.
Shakespeare chose his rhyme schemes purposefully and it is no oversight that the witches speak in rhyme, for example:
Fair is foul, an foul is fair:
Hover through the fog and air.
There can be no mistaking that Shakespeare, who introduces the witches first in Macbeth, chose to intensify their characterization by using rhyming couplets when they appear. This increases the pace and adds to the importance of the witches in establishing the plot. Rhymes are easy to remember and the witches will stay in our thoughts throughout, due to this. Famous quotes become relevant in many instances.
How many children ( and parents) realize that they are quoting Macbeth when they use famous words, such as "Double, double toil and trouble; / Fire burn, and cauldron bubble," a favorite of parents when creating atmosphere in bedtime stories?
Atmosphere is paramount in drama and without it, some scenes would lose significance. Blank verse is Shakespeare's work of choice but he carefully moulds his audience in the development of characters.
Shakespeare ... puts prose rather than verse into the mouths of the insane, and Lady Macbeth ... as a symptom of her mental disorder.
There can be no mistaking Lady Macbeth's descent into madness and her words hold more significance as we realize that she is losing control. Her use of prose gives the impression, almost, of speaking without purpose, babbling more to herself than to those around her:
Out, damned spot!out, I say!One, two; why then 'tis time..
Shakespeare uses his skill to develop individualism in his characters and we become familiar with the 'style' of a particular character. Rearrangement of words to ensure that it meets with the intention is not unusual.
In Act IV, scene i, Macbeth visits the witches and Shakespeare uses various means to establish their relevance in Macbeth's downfall. Macbeth is so influenced by the witches that he too uses rhyme in amongst his usual verse; "..never be, ? Who can impress the forest, bid the tree"...And even lectures the witches, warning them that they will be cursed. Macbeth's increasing belief in his purpose is reinforced here.
To create a complete picture, Shakespeare adeptly moulds his characters and whether they are viewed from the pages of the play, or acted - which obviously adds its own dimension, - their individuality and personality is assured.