How Shakespeare Presents Ambition in Macbeth

Shakespeare doesn't portray Macbeth as inherently ambitious, but as a tragic hero. He lacks bloodlust yet develops vaulting ambition via metaphysical aid, which leads to an unholy regicide and a tyrannous rule foreseen by the witches.In Macbeth Act 1;5 Lady Macbeth speculates about Macbeth's letter on the prophecies proclaiming t​hat he is 'too full o'th'milk of human kindness' and that 'Thou wouldst be great, art not without ambition, but without the illness should attend it'. 

Lady Macbeth is making use of euphemisms in case she is overheard, she is declaring ​that Macbeth lacks a killer instinct in an accusing tone inferring cowardice effectively emasculating him, milk being a metaphor for a stereotypically feminine quality of nurturing kindness. Lady Macbeth is shown to be witch like with the quote 'That I may pour my spirits in thine ear' she could be literally speaking about malevolent spirits or alternatively she could be referring to her advice being poisonous both of which are demonstrated by the witches. 

The parallels between Lady Macbeth and the witches stretch further, she believes that the ends justify the means, even including regicide, similar to the witches belief that 'fair is foul, and foul is fair'. Even later on this trend continues in the quote 'Out, damned spot'.The word damned suggests that she has been condemned by God to suffer eternal punishment in hell, witches were believed to have a witches mark which appeared like a wart which could explain the oddly specific language.

At the end of the extract Lady Macbeth explains that 'fate and metaphysical aid doth seem to have thee crowned withal'. The word 'seem' suggests that there may be a discrepancy between appearance and reality which she mirrors when she said 'look like th'innocent flower, but be the serpent under't' this suggests that things aren't as they seem meaning that the witches may have an ulterior motive, in which Hecate promises to ruin Macbeth in a tragedy of fate.Macbeth begins to develop a self destructive thirst for power in Act 1 when he declares that '[he has] no spur to prick the sides of his intent, but only vaulting ambition that o'erleaps itself and falls on th'other' which could mean that this ambition is overriding his greater virtues/judgement. 

Later, after the regicide, he explains that 'O, full of scorpions is my mind dear wife' suggesting that Lady Macbeth's poisoning has fully taken a hold of his mind, with the scorpions representing Macbeth's dark desires.In conclusion, Macbeth's pursuit of power corrupted him as Lady Macbeth explains that ambition often comes with an illness to attend it - a constant thirst for power spawning a tyrant of catastrophic consequences. To gain something you must lose something, in this case it was his humanity.