The milk of human kindness
Glamis thou art, and Cawdor, and shalt be
What thou art promis'd. Yet do I fear thy nature,
It is too full o' th' milk of human kindness
To catch the nearest way.
To Lady Macbeth, the "milk of human kindness" is distasteful
stuff—no self-respecting man has any use for it. Therefore, when we
use the phrase to approve someone's compassion, we reverse the
Lady Macbeth is ambitious, and fears that her milky husband
lacks the mettle to grab the Scottish crown in the most expeditious
manner. "The nearest way," as she sees it, is to murder King
Duncan. She hatches this plot—which had independently occurred to
Macbeth as well—when he writes home that three witches have
prophesied that he would be created "thane" (lord) of Cawdor, and
later would ascend the throne. The first half of the prophecy has
already come true, and Lady Macbeth is in a hurry to make sure the
second half comes true too.
As fluids go, Lady Macbeth is more inclined to murderous blood
than nurturing milk. Later, goading the hesitant Macbeth, she
insists that, if she had sworn to do it, she wouldn't have
hesitated to take her own baby "while it was smiling in my face"
and to "Have pluck'd my nipple from his boneless gums,/ And dash'd
the brains out." A charming woman.