apostolic churches because there is no difference of doctrine. This is our guarantee of truth.26 What, then, is heresy? For Tertullian at least, heresy is teaching that can be identified by its diversity and contrariety. That is, as Tertullian puts it, “it originates neither from an apostle nor from an apostolic man; for the Apostles would not have diverged from one another in doctrine; no more would the apostolic man have put out teaching at variance with that of the Apostles.”27 Irenaeus, a gifted
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