Ask Your Favorite Muslim

[Rayaan]

What criteria do you use to discern sincere belief from insincere belief?

There are some criterias but they are highly subjective. Also, the most important thing to remember is that we can't ever know for sure who actually believes and who doesn't. See my last comments in this post (in response to Aegon).

Those are pretty vague, not to mention that they could easily be used by those you think aren't real in reference to you.

There's a lot more description about the munafiqs than what I posted. See this for example:

http://islam2011.tumblr.com/post/6152214...ned-in-the

Also, here's a talk where a shaykh goes through some of the core characteristics of munafiqs mentioned in the Quran:

So, do you think extremists would fall under this category of "munafiqs"?

I don't think that extremists are necessarily munafiqs, though they could be. It's not possible to know with 100% certainty whether or not someone is lying about his faith anyway. That's why, generally, we should take people's own words about what they claim to be.

That said, if someone does display many of the characteristics or "signs" of munafiqs as described in the Quran, then I should start being more careful of that person, although he still might be a Muslim. And, either way, what is important is that I still have to talk, act, and treat him like a Muslim. Only God alone has certainty about people's faith or lack thereof.