Task: Question Generation
Input (English): The use of the word "heresy" was given wide currency by Irenaeus in his 2nd century tract Contra Haereses (Against Heresies) to describe and discredit his opponents during the early centuries of the Christian community.[citation needed] He described the community's beliefs and doctrines as orthodox (from ὀρθός, orthos "straight" + δόξα, doxa "belief") and the Gnostics' teachings as heretical.[citation needed] He also pointed out the concept of apostolic succession to support his arguments.
Output (English): What concept did Irenaeus cite to help support his arguments?