Abstract: An hypothesis: Socrates, according to the Socratics, judged sôphrosunê (‘discipline’) to be the fundamental virtue; debate ensued about the sense of fundamentality – e.g., as a condition for the other virtues, as category subsuming the others, etc. The best evidence for the hypothesis comes from Xenophon, Plato, Antisthenes, and indirectly from Aristophanes. This presentation focuses on the first of these authors, specifically two arguments about sôphrosunê attributed to Socrates in Xenophon’s Memorabilia. The shorter is Socrates’ conflation of sophia and sôphrosunê (3.9.4); the longer, called the first stage in Socrates’ curriculum, is Socrates’ explanation of sôphrosunê by teaching Euthydemus to have sôphrosunê peri theous, “regarding the gods” (4.3). Socrates’ position, I argue, is that sôphrosunê is the capacity to acknowledge authoritative norms – to be committed to them as action-guiding. This may justify our calling sôphrosunê, for the Socratics, the virtue of agency.