 To understand Caesar’s crossing of the Rubicon against the background of Republican law is to understand the crossing as transgressing not a law of nature (natural laws apply uniformly to the present, past, and future), but a military norm which banned armed generals from crossing a border (norms, unlike natural laws, change from time to time). Understanding actions historically requires understanding them more like responses to commands that may be followed or disregarded, than as instances (or counter instances) of empirical laws. When understood historically, therefore, the actions of past agents are explained more in the manner in which one understands the action of a motorist who stops at a traffic light (i.e., as abiding by a traffic regulation) than they are in the way in which an astronomer retrodicts the death of a star. The mindset of past agents cannot be investigated under the presupposition which governs empirical science, i.e., the uniformity of nature, because the study of mind, is a “normative or criteriological enquiry” (PA: 171, footnote).