Milk Of Human Kindness

The first published version of this phrase appears in William Shakespeare’s play Macbeth written sometime between 1603 and 1607.  In Act 1, Scene 5 when Lady Macbeth complains that her husband isn’t ruthless enough with his rivals.

LADY MACBETH
Yet do I fear thy nature; It is too full o’ the milk of human kindness.

Lady Macbeth belittles her husband’s courage and manhood, countering his arguments about sparing Scottish King Duncan’s life until Macbeth finally relents and agrees with her that they should kill their overnight guest.  Of course, from that point on, Macbeth needs no encouragement from his lady to continue with his plans to secure the throne for himself.

There’s a fair bit of discussion about the milk of human kindness in the Old Testament of the Bible however, contrary to popular belief, the phrase itself never appears.