In describing "Thinking" (logic-judgements) van der Hoop writes:
(b) This ordered world of thought is not, however, isolated from reality. It reflects the relationships and facts of reality; but since, in doing so, it has regard only to the more essential and constant factors, we obtain a more reliable picture than our total experience provides.
(c) This reliability is the consequence of the fact that the structures of the sphere of thought have been built up by humanity in the course of centuries, so that the experience of endless generations is contained within them. The use of these structures is part of our education, and from youth up we are accustomed to regard them as possessing universal validity.
(d) The constancy of thought-images is the result of abstraction. Observations and ideas are abstracted from instinctive and intuitive experience, by the isolation of common features from the content of various experiences. According to the stage which this process of abstraction has reached, there may be all kinds of transitional forms between thought-forms and those of intuition or sensation. Starting from certain thought-forms, we may, by filling out these forms with every detail, undo the work of abstraction, and work back to the forms characteristic of sensation and intuition.
The most important line here (to me) is "Observations and ideas are abstracted from instinctive and intuitive experience, by the isolation of common features from the content of various experiences." By "instinctive" he means S(ensory, he disagrees with Jung), and intuitive is N. The main point of thought, where it differentiates from perception would then be "isolation of common features", coming from what was perceived.
As Spock would say "facinating". (Spock was INTP, an introverted thinker.)