The Thinker type is a type that values logic and objectivity above almost anything else. They are highly logical and analyze objects, events and statements by using reason – the decisions are made based to bring the best outcome result based on analysis. They consider themselves quite reasonable and question people, events, things etc… if they do not make proper logical sense, being quite critical specially due to a constant evaluation of things. Their relationships are primarily task-focused and they usually expect others to be consistent with what they already know.
People from this type are constantly analyzing things: Does this make sense? What is the best approach for this situation? Is there any theory or practice that can help and aid this task? What are the pros and cons of this decision? The Thinking type has also a tendency to be impersonal and firm on the judgments they made (after they are properly evaluated the situation).
“There is no Extraversion or Introversion here?” Yes, there is no E/I for this type. E/I on this type is undifferentiated, reactive and adaptive: Whatever the attitude of E/I is dictated by environment & conditions, society demands and there is a tendency also for this type to alternate between one approach or the other. This type is a “stage 1” in differentiation terms and that means that this type has generally a weak sense of self, due to being adaptive on the E/I attitude and lacking an auxiliary function (this type does not have a particular preference for intuition or sensing). Basically, for this type, socialization is made by whatever is the most logical decision, concepts and facts are evaluated and used conform to the light of logic.
JUNG DESCRIPTION OF THINKING (there is no Jung description for the thinker type)
53. THINKING. This I regard as one of the four basic psychological functions (q.v.). Thinking is the psychological function which, following its own laws, brings the contents of ideation into conceptual connection with one another. It is an apperceptive (q.v.) activity, and as such may be divided into active and passive thinking. Active thinking is an act of the will (q.v.), passive thinking is a mere occurrence. In the former case, I submit the contents of ideation to a voluntary act of judgment; in the latter, conceptual connections establish themselves of their own accord, and judgments are formed that may even contradict my intention. They are not consonant with my aim and therefore, for me, lack any sense of direction, although I may afterwards recognize their directedness through an act of active apperception. Active thinking, accordingly, would correspond to my concept of directed thinking.85 Passive thinking was inadequately described in my previous work as “fantasy thinking.”86 Today I would call it intuitive thinking.
To my mind, a mere stringing together of ideas, such as is described by certain psychologists as associative thinking,87 is not thinking at all, but mere ideation. The term “thinking” should, in my view, be confined to the linking up of ideas by means of a concept, in other words, to an act of judgment, no matter whether this act is intentional or not.
The capacity for directed thinking I call intellect; the capacity for passive or undirected thinking I call intellectual intuition. Further, I call directed thinking a rational (q.v.) function, because it arranges the contents of ideation under concepts in accordance with a rational norm of which I am conscious. Undirected thinking is in my view an irrational (q.v.) function, because it arranges and judges the contents of ideation by norms of which I am not conscious and therefore cannot recognize as being in accord with reason. Subsequently I may be able to recognize that the intuitive act of judgment accorded with reason, although it came about in a way that appears to me irrational.
Thinking that is governed by feeling (q.v.) I do not regard as intuitive thinking, but as a thinking dependent on feeling; it does not follow its own logical principle but is subordinated to the principle of feeling. In such thinking the laws of logic are only ostensibly present; in reality they are suspended in favour of the aims of feeling.
53a. THOUGHT. Thought is the specific content or material of the thinking function, discriminated by thinking (q.v.).”
Typology Triad 