On Fasting

De Ieiunio (On Fasting, Against the Psychics) belongs to Tertullian's Montanist period, written after his break with the mainstream congregation at Carthage. The treatise defends the New Prophecy's practice of extended and more rigorous fasting — including fixed fast days and xerophagies, periods of dry eating that excluded meat, wine, and succulent foods — against Christians he derisively calls psychici, those he accuses of living according to the flesh rather than the spirit. The work is a polemic born of a concrete dispute: how much fasting the church should require, and who has authority to set it.

Tertullian argues his case almost entirely from scriptural precedent, marshaling Moses, Elijah, Daniel, John the Baptist, and Christ's own forty days in the wilderness to show that rigorous abstinence marks every serious encounter with God. He turns repeatedly to the charge that his opponents feast when they should mourn, indulging appetite while calling restraint legalistic innovation. Running through the treatise is a sharp dualism between flesh and spirit: satiety, he insists, dulls spiritual perception and opens the door to sin, while hunger disciplines the body into readiness for revelation. He also defends the Montanist claim that the Paraclete may enjoin new disciplines beyond what earlier custom established, a claim that put him at odds with bishops who saw such additions as presumption rather than prophecy.

The treatise matters now chiefly as a document of controversy rather than settled teaching. It preserves one of the few firsthand accounts of Montanist ascetic practice and of the resistance it provoked, showing a church still negotiating the boundaries between charismatic authority and institutional custom, and between voluntary devotion and binding law. It also displays Tertullian's rhetorical temperament at its most combative — brilliant in its command of Scripture, unsparing in its contempt for opponents, and unembarrassed about reading bodily discipline as a direct measure of spiritual seriousness. Read alongside his earlier, more moderate writings, it shows how far his thought moved once he judged the mainstream church too lax.

Who should read this: students of patristics and early Montanism, and anyone tracing the history of Christian fasting practice and the tensions between prophetic charism and ecclesial order. It is not a devotional text and offers little pastoral comfort; its harshness toward fellow Christians requires a reader prepared to weigh its arguments historically rather than take its judgments as representative of the wider early church.