In "Macbeth," Shakespeare uses iambic pentameter to convey the natural flow of the English language while maintaining a sense of poetic structure. However, it's worth noting that not all lines in the play strictly adhere to iambic pentameter. Shakespeare frequently employs variations in meter to add emphasis or create dramatic effects. Here's an example from Act 1, Scene 1, where the Witches speak in iambic pentameter. "When shall we three meet again? In thunder, lightning, or in rain?" In these lines, each line consists of five metrical feet, with each foot containing an unstressed syllable followed by a stressed syllable. This creates the rhythmic pattern typical of iambic pentameter.
Throughout "Macbeth," Shakespeare maintains this pattern in many of the characters' dialogues, including Macbeth himself. However, he also skillfully varies the meter at times, using trochaic feet (stressed followed by unstressed syllables) or spondaic feet (two stressed syllables) to create moments of emphasis or to reflect the characters' emotional states.