“Religious authority” remains a ubiquitous but controversial term of comparative analysis. In Islamic studies, authority is generally personified in the form of the ulama and most often viewed through Weber’s lens of charismatic, legal-rational, and traditional types of legitimate domination. Our particular interest, Twelver Shi‘i Islam, seems a paradigmatic case, where the relationship between “the Ayatollahs” and state power has dominated academic discussion since Khomeini. Through ethnography of a Shi‘i diaspora community in the UK, we argue for a radical shift in perspective: away from forms of clerical power and towards non-specialist uses of clerical authority as expert opinion. Far from such “epistemic” authority being opposed to ordinary agency, here they are inextricably linked. Inspirational work in the anthropology of Islam has understood ordinary Muslim experiences of authority in non-liberal ways, as (Foucauldian) ethical discipline and self-care. We maintain the need to transcend not only domination but discipline too, refocusing the comparison between (Shi‘i) Islamic legal and liberal thought, in the form of Raz’s classic “service conception” of authority. Both stress the rationality of following authoritative opinion and its role as reason and justification for individual action. Our ethnography of ordinary practice then shows the sheer diversity of ways that such epistemic authority can be taken up, including, but not limited to, projects of personal piety and adversarial community politics. In our context, as surely also in others, domination and discipline should thus be seen as potential uses of “religious” epistemic authority, rather than as its privileged form.