How do you define a false teacher? 

SPROUL: When is a false teacher a false teacher? It's when he teaches falsehood.

MOHLER: Amen. I would just add that I think there is in the New Testament a clear reservation of that title not just for one who teaches falsely but for one who is uncorrectable and who resists correction.

Apollos was a false teacher. But when he was taught how to preach a better way, how to be more faithful to Scripture, he was corrected (Acts 18:24-28).

So there's a difference between a false teaching and a false teacher. Because just about any preacher, especially one who is just starting out, is going to teach something that's false. That's quite different than being a false teacher: uncorrected and uncorrectable.

SPROUL: And the chief characteristic of his teaching is falsehood.

We all err. Calvin said no theologian is ever more than eighty percent right. The problem is we don't know which that twenty percent is. And then for some of us it's fifty or sixty percent.

MACARTHUR: I think we need to say that there are some absolutely non-negotiable truths that you are false to teach: if you deny the Trinity, if you deny the deity of Christ, if you deny His sinless life and substitutionary death, salvation by grace through faith, the gospel. That's the drivetrain of truth, saving truth. Those are not negotiable. You can misunderstand baptism or something like that.

SPROUL: Those we call errors, not heresies. There's a difference between error and heresy. Heresy is something that strikes at the very heart of the gospel and of the truth.

Lightly edited for readability, this is a transcript of  John MacArthur's, Albert Mohler's, and R.C. Sproul's answers given at our 2017 National Conference. To ask Ligonier a biblical or theological question, just visit Ask.Ligonier.org or message us on Facebook or Twitter.