Davidson and others have recommended principles of charity. In this article I am defending their claim that interpretation and the explanation of action are impossible without a rather strong principles of charity. The principle of charity in the domain of interpretation is that when we interprete what others say we must assume their beliefs are usually true. The principle of charity in explaning action says that the speaker must generally be rational both in the sense that his beliefs must be logical and in the sense that his action must be reasonable given his desires and beliefs. These principles should be considered as constitutive for interpretation and the explanation of action by using such concepts as desires, beliefs and other attitudes.