Here is a translation into Modern English for the phrase under question:
- "Where civil blood makes civil hands unclean" = The blood of the citizens of Verona makes the hands of the citizens both bloody and uncivilized; that is, not polite, and possibly murderous. [Please see further explanation below]
In the first Prologue to Romeo and Juliet, William Shakespeare provides a brief summary of the action. This summary identifies the main parts of the drama for audiences. (Prologues were given especially for the groundlings of Shakespeare's time who were uneducated and needed things to be explained simply.) Shakespeare, then, lets the audience know that the setting of his tragedy is in Verona and what action occurs in the opening scene is affected by an old feud between the Montagues and the Capulets--"ancient grudge"-- a feud that the citizens renew as they bloody their hands from wounds which they inflict upon the other citizens who are their old enemies:
From ancient grudge break to new mutiny,
Where civil blood makes civil hands unclean.
In addition there may be some wordplay upon the word civil. Whereas "civil" relates to a community of ordinary citizens, the pun may include the other meaning of being polite and civilized. Thus, "civil blood" has the meaning of the blood of citizens, but "civil hands unclean" can have a double meaning:
- Literal meaning, or denotation: The citizens have blood on them and are not clean--"civil blood"
- Implied meaning, or connotation: Such hands are not those of truly civilized (polite and mannerly) men--"civil hands unclean."
So, with the double meaning attached to this phrase, Shakespeare suggests the bloodshed to come in his play between citizens of the two feuding families, who lose their civility (polite behavior) in their hatred for each other.