One of the principles I try to live my life by is "Does that even make sense?" It's a good rule, because it keeps me out of a lot of trouble and is a great way to cut through the Stupid.
(Usually, there's an f-bomb in there, but I'm trying to keep this clean, so as not to distract from the philosophical point.)
It's kind of like detective work, or maybe just like thinking, like at all.
If someone says something, for example, the sky is green, then "Hey, does that even make sense?" I mean, I can look and usually the sky is blue, or white, or a murky shade of grey, depending on the rain, so I highly doubt it was actually green. Now, I'm open to the idea that the lighting of the moment, or the beer bottle the person was looking through made the sky appear green, but that's not the same thing. The latter, however, is an example of me using my brain to help me make sense of what this person is saying. (In this example, the speaker is most likely pulling my leg, but you already knew that one, so I had to offer something else, because my secret agenda is to get you thinking.)
Now, we can go to another example, such as "All Christians are good and kind people." Well, basic experience says that is wrong, too, since Christian People are People-who-happen-to-be-Christian, and you can't take the Pee out of People, so that doesn't make sense.
But, now you're comfort zone is a bit rattled, and you're trying to figure out which part of that last paragraph I'm referring to when I say "that doesn't make sense."