Cognitive functions can be divided into two categories – Rational (Judging) and Irrational (Perceiving). The two Rational functions are Thinking and Feeling. The two Irrational functions are Sensation and Intuition. Each of the four functions can be of two types based on their focus – Extroverted (focused on object) and Introverted (focused on subject). Here, the person is the subject and what the person observes or puts judgement on is the object.
Every person has all eight cognitive functions and their relative preference and development makes each personality unique (and also the way they are used). We take all the functions into account and choose the four most preferred and developed ones to evaluate the most probable MBTI type of an individual. Our choice here is, however, constrained by the idea of the functional axes.
A rational function or an irrational function cannot work alone; it needs the other. For example – Thinking needs Feeling, and Sensation needs Intuition. If you only used Thinking, you wouldn’t do anything as you wouldn’t give a value judgement on what should be done or decide what you want to do. On the other hand, if you only used Feeling, you couldn’t do anything as you couldn’t decide what’s the best way to do what you want to do.
This brings into picture the functional axes – Judgement axes (Te-Fi, Fe-Ti), and Perception axes (Se-Ni, Ne-Si). Here, T, F, S, N represent Thinking, Feeling, Sensation, and Intuition respectively. The ‘e’ and ‘i’ are for extroverted and introverted, as the introversion and extroversion need to be balanced as well. No one is purely introverted or extroverted.
In an MBTI type two axes have to be present – a judgement axis and a perception axis – one enveloping the other. This is to be noted while choosing the first four functions to represent one’s probable MBTI type. Four letters represent an MBTI type, and the four places can have one of two variables each, taking the total to 16 MBTI types.
The first (I, E) letter represents the focus of the first function – introverted or extroverted – and does not simply state whether a person is outgoing or reserved. The second (S, N) and third (T, F) letters represent the first perceiving and judging functions among the top four functions of the type respectively. The fourth (J, P) letter shows whether the first extroverted function is judging or perceiving, and does not simply state whether a person is active or lazy. For example, my MBTI type is INTJ. The functions are – Ni, Te, Fi, Se. The axes are – Ni-Se enveloping Te-Fi.
If you have a function – introverted or extroverted – developed, there’s a good chance that its extroverted or introverted counterpart is also developed. You’ll see this in the cognitive functions’ diagrams of the MBTI types, with each function slightly extended into the other side.
(Ignore the bad handwriting and drawing)