Particular attention has been paid in the present century (notably by Mr. E. F. Carritt, the late Professor Pritchard, and Sir David Ross) to the question as to whether a man's duty is to do what is actually right, i.e. what his situation actually demands of him, or what he thinks is right. Mr. Carritt has pointed out that the former possibility bifurcates—a man's duty may be to do what is actually demanded by his actual situation, or what is (or would be) actually demanded by what he believes to be his situation. (The latter possibility also bifurcates—a man's duty may be to do what he thinks is demanded by what he believes to be his situation, or what he would think was demanded by his actual situation, if he knew it; but only the first of these alternatives has been or needs to be seriously considered.) I do not propose in the present paper to carry this discussion any further, but rather to consider how it has been carried on in the past, as there seems to be a little confusion on this point.