These lines are equally remarkable for a tone of settled assurance as to the fulfilment of the speaker’s royal hope, and for an entire absence of any expression of reliance upon the power of the witches,—­the hitherto supposed originators of that hope,—­in aiding its consummation.  It is particularly noticeable that Macbeth should make no reference whatever, not even in thought, (that is, in soliloquy) to any supernatural agency during the long period intervening between the fulfilment of the two prophecies.  Is it probable that this would have been the case had Shakspere intended that such an agency should be understood to have been the first motive and mainspring of that deed, which, with all its accompanying struggles of conscience, he has so minutely pictured to us as having been, during that period, enacted?  But besides this negative argument, we have a positive one for his non-reliance upon their promises in the fact that he attempts to outwit them by the murder of Fleance even after the fulfilment of the second prophecy.

The fifth scene opens with Lady Macbeth’s perusal of her husband’s narration of his interview with the witches.  The order of our investigation requires the postponement of comment upon the contents of this letter.  We leave it for the present, merely cautioning the reader against taking up any hasty objections to a very important clause in the enunciation of our view by reminding him that, contrary to Shakspere’s custom in ordinary cases, we are made acquainted only with a portion of the missive in question.  Let us then proceed to consider the soliloquy which immediately follows the perusal of this letter: 

        “I do fear thy nature. 
  It is too full o’ the milk of human kindness,
  To catch the nearest way:  thou wouldst be great;
  Art not without ambition; but without
  The illness should attend it.  That thou wouldst highly,
  That wouldst thou holily; wouldst not play false
  And yet wouldst wrongly win:  thou’dst have, great Glamis,
  That which cries this thou must do if thou have it,
  And that which rather thou dost fear to do,
  Thou wishest should be undone.”

It is vividly apparent that this passage indicates a knowledge of the character it depicts, which is far too intimate to allow of its being other than a direct inference from facts connected with previous communications upon similar topics between the speaker and the writer:  unless, indeed, we assume that in this instance Shakspere has notably departed from his usual principles of characterization, in having invested Lady Macbeth with an amount of philosophical acuteness, and a faculty of deduction, much beyond those pretended to by any other of the female creations of the same author.