That's another thing, and a great topic starter. Many people know what they want to say, but can't properly say it.
An obvious example would be people with disabilities. In my first block class every other day, there is a mute person in my class. Also, he cannot walk, or see. However, we know he is no less intelligent than us. He can understand English very well, he has a great sense of humor, and he is quite intelligent. He's going to write (well not write but sort of "talk" out) a large essay in about a week. I can't wait to read what he has to say.
Now don't think of me as a self-pitying asshole for this next part, I am merely using myself as an example. When I get into an argument, I think of great arguments against my opponent. But, I have trouble wording them effectively. This lets the other person twist it around and kill my side with it. I know what I want to say, but I can't say it.
In both scenarios you have normal people who have hit a sort of roadblock. This doesn't mean they're dumb, or special, or anything. Theoretically, they are normal. They just need a bit of help. So how can somebody be sure if He is as smart as I am? Or if I am as smart as HE is? What can we do to measure intelligence for people with disablities of that kind?