Even in the awful scene where her imagination breaks loose in sleep she uses no such images as Macbeth’s.  It is the direct appeal of the facts to sense that has fastened on her memory.  The ghastly realism of ’Yet who would have thought the old man to have had so much blood in him?’ or ‘Here’s the smell of the blood still,’ is wholly unlike him.  Her most poetical words, ’All the perfumes of Arabia will not sweeten this little hand,’ are equally unlike his words about great Neptune’s ocean.  Hers, like some of her other speeches, are the more moving, from their greater simplicity and because they seem to tell of that self-restraint in suffering which is so totally lacking in him; but there is in them comparatively little of imagination.  If we consider most of the passages to which I have referred, we shall find that the quality which moves our admiration is courage or force of will.

This want of imagination, though it helps to make Lady Macbeth strong for immediate action, is fatal to her.  If she does not feel beforehand the cruelty of Duncan’s murder, this is mainly because she hardly imagines the act, or at most imagines its outward show, ’the motion of a muscle this way or that.’  Nor does she in the least foresee those inward consequences which reveal themselves immediately in her husband, and less quickly in herself.  It is often said that she understands him well.  Had she done so, she never would have urged him on.  She knows that he is given to strange fancies; but, not realising what they spring from, she has no idea either that they may gain such power as to ruin the scheme, or that, while they mean present weakness, they mean also perception of the future.  At one point in the murder scene the force of his imagination impresses her, and for a moment she is startled; a light threatens to break on her: 

                  These deeds must not be thought
     After these ways:  so, it will make us mad,

she says, with a sudden and great seriousness.  And when he goes panting on, ‘Methought I heard a voice cry, “Sleep no more,"’ ... she breaks in, ‘What do you mean?’ half-doubting whether this was not a real voice that he heard.  Then, almost directly, she recovers herself, convinced of the vanity of his fancy.  Nor does she understand herself any better than him.  She never suspects that these deeds must be thought after these ways; that her facile realism,

     A little water clears us of this deed,

will one day be answered by herself, ‘Will these hands ne’er be clean?’ or that the fatal commonplace, ‘What’s done is done,’ will make way for her last despairing sentence, ‘What’s done cannot be undone.’