The most obvious device in the soliloquy is apostrophe, in which Lady Macbeth directly addresses and calls on these extra-human "spirits" and "ministers," as well as the "thick night," she believes have the power to give her the qualities needed to commit murder—or at least to spur Macbeth to do...
The most obvious device in the soliloquy is apostrophe, in which Lady Macbeth directly addresses and calls on these extra-human "spirits" and "ministers," as well as the "thick night," she believes have the power to give her the qualities needed to commit murder—or at least to spur Macbeth to do so. Why, one might ask, are these apostrophes necessary when it is quite obvious Lady Macbeth isn't the nicest person in the world? Clearly, Shakespeare is depicting a paradox in her character. The conventional view of Lady Macbeth as an evil woman is in some sense belied by this passage. She is more than conscious of her milder qualities, which she attributes to her femininity:
... unsex me here
And fill me, from the crown to the toe, top-full
Of direst cruelty!
Personification is the device of attributing human characteristics to inanimate things, as in:
Nor heaven peep through the blanket of the dark
To cry "Hold, hold!"
Heaven is thus attributed with the power of sight and speech—unless it is considered a metaphor of God.
This last point brings up the question of whether Lady Macbeth believes in a Divinity, in God. One would think that a person having the need to rhapsodize in this manner must believe in something, but if so the central device that informs the whole soliloquy is irony. Lady Macbeth would obviously not be half as interesting a person without this apparent contradiction in her character between cruelty and regret. The culmination of the paradox established here is the unresolved guilt that causes her to go crazy and, evidently, to commit suicide.
The soliloquy is also an example of hyperbole. Her pleadings and apostrophizing are exaggerated, almost an instance of "protesting too much." This is a typical device of Shakespeare. It's part of his style, and accounts for much of the visceral effect his verse has on us, that his language is extravagant and unrestrained. The most dislikable characters in the Shakespeare canon have a tendency to speak in a manner that is elevated and florid, even by the standards of his time. And this, too, contributes to the irony of the passage.