Socionics

So cognitive function isn't MBTI, which is vast simplification and is basically like astrology. The MBTI is too rigid, there is no flexibility in the system (actually, it doesn't really contain any system per se) apart from 16 stereotypes.

Jung himself didn't really delve too deeply into each cognitive function in his original writings, I believe. He was merely describing people that he observed during his work, which he organized into four types of people: a Feeling type person, a Thinking type person, etc. Cognitive functions, and how they systemically interact with one another, evolved from Jung's writings to address what each cognitive function is and how they interact together systemically with one another, to best model how a human being might operate mentally to understand and navigate the world.

There are indeed only four cognitive functions (Judgment functions of Thinking, Feeling; perceiving functions of Sensing, Intuition), each with two kinds of orientation (inwards or outwards: e.g. Extroverted Thinking, Introverted Thinking). If oriented inwards, the function works in an introspective and subjective way; if oriented outwards, then outwards from the self, looking into the external world, more "objective", less idiosyncratic.

For each person, the idea is there must be a primary perception function and a primarily judgment function that work in tandem, always oriented in opposite directions. For example, if person X has a dominant cognitive function of Extraverted Sensation--they are maximally geared towards perceiving physical phenomena and information objectively, without any preconditions or filter--then it makes sense that the next function must inevitably be a judgment function oriented inwards (say, Introverted Feeling), to sort through all the raw information X accumulates in bulk, process them so X can form a subjective understanding of the world and how it works, how X feels about it, etc. In cognitive function, X would be an Extraverted Sensation Introverted Feeling person, or SeFi, or ESFP in MBTI lingo.

The system further assumes that X must also have an INTROVERTED sensing function (to manage their subjective, filtered, perceptions) and an EXTRAVERTED judgment function (to execute decisionmaking into the world), at lower dominance/level of consciousness and complemental to the other two. So the full cognitive expression for the ESFP would be (Extraverted Sensation) then (Introverted Feeling) then (Extraverted Thinking) then (Introverted Intuition) = Se Fi Te Ii

Oops I wrote too much ! 😅