"In Macbeth, the poet's object was to raise the mind at once to the high tragic tone, that the audience might be ready for the precipitate consummation of guilt in the early part of the play. The true reason for the first appearance of the Witches is to strike the key-note of the character of the whole drama, as is proved by their re-appearance in the third scene, after such an order of the king's as establishes their supernatural power of imagination. I say information, -- for so it only is as to Glamis and Cawdor; the 'king hereafter' was still contingent, -- still in Macbeth's moral will; although, if he should yield to the temptation, and thus forfeit his free agency, the link of cause and effect more physico would then commence. I need not say, that the general idea is all that can be required from the poet, -- not a scholastic logical consistency in all the parts so as to meet metaphysical objectors. But O! how truly Shakspearian is the opening of Macbeth's character given in the unpossessedness of Banquo's mind, wholly present to the present object, -- and unsullied, unscarified mirror! -- And how strictly true to nature it is, that Banquo, and not Macbeth himself, directs our notice to the effect produced on Macbeth's mind, rendered temptible by previous dalliance of the fancy with ambitious thoughts:
Good Sir, why do you start; and seem to fear Things that do sound so fair?
[Henry Nelson Coleridge, ed. The Literary Remains of Samuel Taylor Coleridge. London: William Pickering, 1836. New York: AMS, 1967: 238-9.]