Quote Originally Posted by Minde View Post
But aren't functions and quadra values manifested in external traits?
No, they are manifested in motivation and thought process, which is precisely why it's so hard to type people. If it was about external traits, like MBTI, this wouldn't be nearly as hard.

How else is one supposed to determine (or even approximate) a person's type without observing behavior?
Obviously behavior is observed and taken into account, but you have to analyze a little more than that. You have to be at least a little bit presumptuous whenever you type someone unless you REALLY know them that well.