How not to be contentious, but to hold up the truth while following Eph 5 in exposing the works of darkness and Titus 1 in silencing "rebellious people, idle talkers, and deceivers"? Here are my suggestions, slightly edited, given to a friend who asked, as we discussed the issue by email.
1. Don't give them room or space to speak. If somebody's teaching false doctrine, don't let them speak at all, on any subject, for they'll get their point of view in somehow.
2. Don't sound mad or irritated. Make sure love for truth and people come across.
3. Don't make it personal. It's not who, but what is being taught.
4. Be direct about it. We (speaking generically) tend to beat around the bush.
5. Nip it in the bud. It's easier to do when there's a few. When it's the majority or a large number, it's harder.
What ideas might you share?