IT - Introverted Thinking

Is fed from subjective and unconscious roots—archetypes.

Depends upon the abstract idea as the decisive factor, and values facts chiefly as illustrative proofs of the idea.

Relies on the thinker's powers of observation and appreciation and use of the inner wealth of inherited experience for soundness and value.

Has as its goal formulating questions, creating theories, opening up prospects, yielding insight, and finally, seeing how external facts fit into the framework of the idea or theory it has created.

Seizes upon the similarities of the concrete case, dismissing irrelevancies.

Has a tendencies to neglect facts or coerce them into agreement with the idea, selecting only those that support the idea.

Consists of an inner thought activity, tied loosely if at all to the stream of sense impressions, which are dimmed by the vividness of the stream of inner impressions.

Myers, "Gifts Differing: Understanding Personality Type"

Introverted Thinking (Ti) utilizes deep and nuanced logic to examine techniques, problems, concepts, or theories. It seeks self-regulation and self-optimization through the development of personal skills, methods, and strategies. It takes a skeptical and reductive approach toward knowledge.

A.J. Drenth, "My True Type: Clarifying Your Personality Type, Preferences & Functions"

Ideologue Ti:

Stubborn on principles. Stick to singular, most-worthy framework that can explain everything. Define precisely. Provide expert logic and guidance. Bring order to ideas. Correct errors, poor-thinking and wrong approaches.

Systemist Ti: 

Take multiple points of view. Find patterns in the chaos. Notice how systems scale, and apply principles in a fluid way. People, art, nature and technology all intercorrelate. Understand and find leverage in the messiness of life. 

Dario Nardi, The Magic Diamond: Jung's 8 Paths For Self-Coaching