It is a mistake to believe that a science consists in nothing but conclusively proved propositions, and it is unjust to demand that it should. It is a demand only made by those who feel a craving for authority in some form and a need to replace the religious catechism by something else, even if it be a scientific one. Science in its catechism has but few apodictic precepts; it consists mainly of statements which it has developed to varying degrees of probability. The capacity to be content with these approximations to certainty and the ability to carry on constructive work despite the lack of final confirmation are actually a mark of the scientific habit of mind. -- Sigmund Freud
Isn't this Socionics in a nutshell?
But really, I have to agree with Freud in this aspect. Ideas do not need measurable proof to be used constructively. Just because you can't see something in a concrete form, doesn't mean it doesn't exist. A speculation is just as valid as a proven fact. If it wasn't, society would still be in the stone age. In fact, most great discoveries began as simple speculations, and guess what? Socionics is just a speculation. Yet it works enough to help people out.
Your INTp friend,