Experts in cognitive domains differ from non-experts in how they represent problems and knowledge, and in their epistemic understandings of tasks in their domain of expertise. This study investigates whether task-specific epistemic understanding also underlies the representation of knowledge on an everyday reasoning task on which the competent reasoners have neither expert domain knowledge nor training. 180 people on jury duty were assessed for epistemological understanding about the nature of knowledge and knowing in general, understanding of the specific task of the juror, and level of argument skill and evidence representation on two jury cases. Epistemic construal of the juror task and task-specific competent reasoning was found related to general epistemology, argument skills, and representation of the evidence. Additionally, estimations of the possibility of certainty in general and in a juror task predicted the participants' expressed certainty about their verdict choices. Implications for developing everyday reasoning competence are discussed. (Contains 6 tables.)