This chapter tackles common stereotypes of the Islamic sharia through a comparative approach, arguing that the history of Christian casuistry provides a rich source for an alternative conceptual vocabulary for describing such rule-dense ethics. In contrast to stereotypes of sharia as ‘strict’, Christian casuistry fell into disrepute as being too lax. This was especially in the form of the doctrine of ‘probabilism’, which allowed the following of any learned opinion, even if not the most widely attested. This was to ameliorate the effects of ‘tutiorism’ – always taking the safest path to salvation. These concepts for discussing the uses of rules are put to work to help understand how contemporary Shi’i Muslims cope with the dilemmas of life in the UK. In questions such as when to break one’s Ramadan fast when a British summer day might last more than twenty hours, or whether one can shake hands with someone of the opposite sex, the rules developed by scholars in the Middle East may not sit well with the realities of life in Britain. Ethnographic fieldwork shows how people take up a variety of tactics in response, whether it be playing it ‘safe’, following a more liberal opinion or using one’s ‘common sense’. Most importantly, rules are neither necessarily rigid nor strict. Rather, legalistic forms of ethics offer a variety of ways to facilitate good conscience, even when faced with the seemingly irreconcilable demands of religious ideals and life in a non-Muslim society.