The idea is simple, and renders simple results: apply Jung's introvert/extravert dichotomy to the functions to get a simple means of differentiating between the black and white shapes.
I know Jung's not Socionics. But neither is 90% of what is said on this forum. Most of the Russian Socionics sites actually take for granted that the reader is already familiar with the fundamental dichotomy between extraversion and introversion, as presented by Jung. I wasn't familiar with the actual difference aside from the surface/superficial. No wonder everything looks like gibberish.
Jung first defines his extraversion/introversion dichotomy as follows:
"The general-attitude types, as I have pointed out more than once, are differentiated by their particular attitude to the object. The introvert's attitude to the object is an abstracting one; at bottom, he is always facing the problem of how libido* can be withdrawn from the object, as though an attempted ascendancy on. the part of the object had to be continually frustrated. The extravert, on the contrary, maintains a positive relation to the object. To such an extent does he affirm its importance that his subjective attitude is continually being orientated by, and related to the object. An fond, the object can never have sufficient value; for him, therefore, its importance must always be paramount."
(Source: Carl Jung, Psychological Types)
Furthermore, he defines the relationship between the subject (I) and the object (You, Him/Her/Them, It) as always a "relationship of adaptation" of which there are two modes of adaptation present in nature - that of the introvert and that of the extravert.:
"At this point a mere general indication must suffice; on the one hand, I need only point to the peculiarity of the extravert, which constantly urges him to spend and propagate himself in every way, and, on the other, to the tendency of the introvert to defend himself against external claims, to conserve himself from any expenditure of energy directly related to the object, thus consolidating for himself the most secure and impregnable position."
(Source: Carl Jung, Psychological Types)
In my own words:
Extraversion - reacts perpetually to the object
Introversion - reacts perpetually from the subject
This is where Myers Briggs gets their "energized by social interaction"/"energized by alone-time" bullshit. Jung goes on to describe the introvert/extravert dichotomy by describing two distinct people. Of course the extravert will be sociable and talkative and the introvert will be reticent and quiet. Most of Jung is metaphorical anyway, and it's safe to bet that the guy is dealing with a less superficial split in the psyche.
This actually works out very well when applied to the functions. Here's what I've got. I've used the hidden agendas to clarify:
"To be loved."
The ability to display the appropriate emotions in response to the situation, as issues present themselves.
The individual's understanding of/identification with man's emotional undercurrent.
The ability to know what/how/which systems must be revised, as the issues reveal themselves.
The individual's understanding of/identification with systems themselves.
"To be wealthy."
The ability to appropriately effect influence on the material world in reaction to the situation, as issues present themselves.
"To be healthy."
The individual's understanding of/identification with the material world.
"To be perfect."
The ability to appropriately manipulate ideas in response to the situation, as issues present themselves.
The individual's understanding of/identification with ideas themselves.
Consequently, I believe that the stronger the introverted version of a function within an individual, the more effectively the extraverted function can work (this is assuming that the extraverted function is in the conscious block of the individual's psyche).
* Jung differentiates his conception of ";ibido" from that of Freud: "[Libido] denotes a desire or impulse which is unchecked by any kind of authority, moral or otherwise. Libido is appetite in its natural state. From the genetic point of view it is bodily needs like hunger, thirst, sleep, and sex, and emotional states or affects, which constitute the essence of libido."
(Source: Carl Jung, The Concept of Libido)