Quote Originally Posted by Expat
I think Rational vs Irrational behavior is much more easily defined and observed.

To really discover if someone is extrovert or introvert, we'd have to get into their heads.

For instance, in the case of and . We can hardly directly experience or observe their and perceptions, but we can easily see how they use . That often makes these types seem "extroverted".
I agree with most of that. I would even like to add, that if you use both functions in your ego block properly, you will even exhibit both introvert and extravert behaviors. This is why most MBTI tests are silly: the ask questions on behavior, and then people get confused and make statements such as "but I'm both introvert and extravert at times, it all depends".

I'm inclined to say that from a Socionic perspective, there is no such thing as an E/I dimesion. In the Big 5 there is, but the Big 5 is about extrenal behavior, not about mental focus.

I'm not sure about your statement on rationality/irrationality. How can you recognize this externally? Typically, I used to think you could tell by people being messy or untidy, but I have found that J-types can be messy as well when they are operating on a neurotic level. MBTI J/P is very similar to Big 5 Conscientiousness, but I think the correlation between Socionics J/P and Conscientiousness is not as strong.