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