On the Detection and Overthrow of the So-Called Gnosis

On the Detection and Overthrow of the So-Called Gnosis, today also called On the Detection and Overthrow of Knowledge Falsely So Called (Greek: Ἔλεγχος καὶ ἀνατροπὴ τῆς ψευδωνύμου γνώσεως, lit. "Elenchus and Overturning of the Pseudonymous Knowledge"), commonly called Against Heresies (Latin: Adversus haereses, Greek: Κατὰ αἱρέσεων), is a five-volume work written by St. Irenaeus in the 2nd century. The final phrase "of knowledge falsely so-called" (Greek: tes pseudonymou gnoseos genitive case; or nominative case pseudonymos gnosis) is a quotation of the apostle Paul's warning against "knowledge falsely so-called" in 1 Timothy 6:20.

Due to its reference to Eleutherus as the current bishop of Rome, the work is usually dated c. 180. In it Irenaeus identifies and describes several schools of gnosticism and contrasts their beliefs with what he describes as catholic (universal), orthodox Christianity. Only fragments of the original Greek text exist, but a complete copy exists in a wooden Latin translation, made shortly after its publication in Greek, and Books IV and V are also present in a literal Armenian translation.

Against Heresies can be dated to sometime between 174 and 189, as the list of the Bishops of Rome includes Eleutherius, but not his successor Victor. Its purpose of was to refute the teachings of various Gnostic groups, specifically what he considers a non-apostolic scriptural exegesis on the part of Gnostics such as Valentinus and others. In this he seeks to present "what was understood as an authentic form of century-old Christian tradition against various forms of Gnosticism."

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