Letter and spirit of the law

The letter of the law versus the spirit of the law is an idiomatic antithesis. When one obeys the letter of the law but not the spirit, one is obeying the literal interpretation of the words (the "letter") of the law, but not necessarily the intent of those who wrote the law. Conversely, when one obeys the spirit of the law but not the letter, one is doing what the authors of the law intended, though not necessarily adhering to the literal wording.

"Law" originally referred to legislative statute, but in the idiom may refer to any kind of rule. Intentionally following the letter of the law but not the spirit may be accomplished through exploiting technicalities, loopholes, and ambiguous language.

William Shakespeare wrote numerous plays dealing with the letter versus spirit antithesis, almost always coming down on the side of "spirit", often forcing villains (who always sided with the letter) to make concessions and remedy. In one of the best known examples, The Merchant of Venice, he introduces the quibble as a plot device to save both the spirit and the letter of the law. The moneylender Shylock has made an agreement with Antonio that if he cannot repay a loan, he will have a pound of flesh from him. When the debt is not repaid in time Portia at first pleads for mercy in a famous speech: "The quality of mercy is not strain'd, It droppeth as the gentle rain from heaven Upon the place beneath. It is twice blest: It blesseth him that gives and him that takes." (IV,i,185). When Shylock refuses, she finally saves Antonio by pointing out that Shylock's agreement with him mentioned no blood, and therefore Shylock can have his pound of flesh only if he sheds no blood.

Interpretations of the U.S. Constitution have historically divided on the "Letter versus Spirit" debate. For example, at the founding, the Federalist Party argued for a looser interpretation of the Constitution, granting Congress broad powers in keeping with the spirit of the broader purpose of some founders (notably including the Federalist founders' purposes). The Federalists would have represented the "spirit" aspect. In contrast, the Democratic-Republicans, who favored a limited federal government, argued for the strict interpretation of the Constitution, arguing that the federal government was granted only those powers enumerated in the Constitution, and nothing not explicitly stated; they represented the "letter" interpretation.

...
Wikipedia