Prichard on Duty and Ignorance of Fact

This paper is an examination of a paper by Prichard, which converted Ross from externalism to internalism. Externalism is the view that agents’ obligations are grounded in features of the situation that they are in. Internalism is the view that agents’ obligations are grounded not in how things actually are, but in how the agent believes them to be. I conclude that Prichard’s arguments are not as powerful as Ross thought; Ross would have done better to stick to his original position. The paper also considers the relevance of a peculiar postscript to Prichard’s paper which was not printed until after his death; it suggests that the postscript does not improve things.