Of course, there is more to the function than the initial shaping, but that is where it begins. It begins in the subjective realm, dealing with psychic content, and being a Thinking function, it's immediate goal is to rationally organize the content into an idea, an idea that is defined and thus clearly constrains the spectrum of possible derivatives from it to a certain set. Incoming data can then be defined as belonging to or not belonging to that set, i.e. true or false, i.e. judging. One's ability to "correctly" do this is more related to actual intelligence or skill. Introverted Thinking dominance is where "libido" (as Jung defines it, mental energy, life energy) is primarily directed to this kind of thought process,
especially to the experience of the shaping, which seems of "paramount importance" to do. Due to repeated practice, Introverted Thinkers become acquainted with a more intensive understanding of and use of this process by way of their fascination with it, and thus may develop actual skill. Over time, Ti dominants become familiar with the "contours of thought."
*edit:
BUT EVEN MORE TO MY POINT:
"But just as little as it is given to extraverted thinking to wrest a really sound inductive idea from concrete facts or ever to create new ones, does it lie in the power of introverted thinking to translate its original image into an idea adequately adapted to the facts. For, as in the former case the purely empirical heaping together of facts paralyses thought and smothers their meaning, so in the latter case introverted thinking shows a dangerous tendency [p. 482] to coerce facts into the shape of its image,
or by ignoring them altogether, to unfold its phantasy image in freedom. In such a case, it will be impossible for the presented idea to deny its origin from the dim archaic image. There will cling to it a certain mythological character that we are prone to interpret as 'originality', or in more pronounced cases' as mere whimsicality; since its archaic character is not transparent as such to specialists unfamiliar with mythological motives. "