Sooo, I've been putting together some potential function look-a-likes. It's pretty rough, but I think the main ideas come across.
Where cognitive processes can look alike.
This describes ways in which cognitive processes might be confused. This is NOT describing functions in whole, just aspects where they might be confused for another one. These are certainly not the only ways functions can be confused either. I think these examples are pertinent in P/J confusion though (ie. determining if you're TiSe or SiTe).
Se + Te
Similarities = both focus on external data, facts, information
Differences = Te is a judging process, focused on categorizing these things logically, using external measures. Te thinking focuses on applying systematized knowledge. Se is a perceiving process, and does not reason, but is aware, focused on finding more & more sensory & factual data to experience. Se thinking is focused on their reactions to these experiences, and these are pursued for their own sake. Negative experience/information may even be sought out, just to see what it is like.
Silly illustration (which personifies the functions): The Te-dom categorizes the sky as blue in color, according to what blue & color are defined as. Se notes the sky is blue & focuses on their immediate instinctive reaction to it.
Ne + Fe
Similarities = both seek to affect people, to get reactions from them
Differences = Fe seeks to affect people to create consensus, to promote harmony or unity of feelings. Fe is a reasoning process, which generally evaluates according to how something affects external relationships. The desire to affect is to keep things in line with their values, values which they determine according to external measures. Fe will generally seek positive reactions, but will take a negative one over nothing, as it may, for example, at least draw attention to their purpose & eventually get people on board.
Ne seeks to affect people so as to impress their ideas on them, to stir the pot, to get a reaction for its own sake, even if negative. Ne is not a rational thought process, but perceives intangible external relationships which imply possibilities, so their thinking is focused on pursuing these ideas, not on creating common value systems or stabilizing relationships. It's a kind of experimentation: how would people respond if I do X?
Silly illustration: Fe believes that the blue sky indicates clean air, and wants to promote the importance of this as it affects the well-being of people. Ne wants to explore the possibility that the sky is not blue, and may say something outrageous to get other people to play along.
Ti & Si
Similarities = similar to Te/Se similarities but introverted. Both deal with facts, knowledge & systems in relation to the inner world.
Differences = Ti is a judging process which creates concepts of what is logical according to an internal measure, using facts & knowledge to create/refine these internal systems. Si is a process which does not reason, but is aware. It collects & stores facts, knowledge & sensory experience according to the impression it leaves on the individual, and that impression is then compared to any future info taken in. Si notes differences, is aware of them, but it does not judge them. Ti judges irregularities to or within their system.
Silly illustration: Ti judges the sky as blue because it is consistent with a color theory they've developed, aided by taking in info (Pe) about color & the sky, etc. Si sees the sky as blue because it appears similar in shade to other things called blue they've seen before OR it sees the sky as "pleasant" because the color implies good weather & clean air (such judgments being very Je), based on their past experience & knowledge of these things.
Fi & Ni
Similarities = both have "visions" amounting to ideals (concepts from the imagination) & deal with the nature of the inner life
Differences = Fi is a reasoning process which evaluates according to an inner ideal, or vision of perfection. These conclusions are viewed by the Fi-dom as personal & used to determine their own needs/preferences, focusing on their individual inner life; how these relate to others is often an aspect of Pe. Fi judges what should be the essence of perfection, creating models of the ideal.
Ni is a perceiving process which becomes aware of concepts & sees how they should or will develop. These ideals are often viewed as objective in the sense that the Ni type does not relate them to him/herself, not focusing on their personal inner life, but the inner nature of things in general. The Ni type may see these ideals as having the universal validity of truth. Ni sees the model essence of all things, viewing them reduced to their most basic concept & then seeing how they relate to one another.
Silly illustration: Fi judges the color of the sky as it relates to their pleasure & needs, and sometimes, by extension, the pleasure & needs of humanity. A grey sky is sometimes pleasing because it reflects an introspective mood Fi enjoys. Ni sees the color blue as a symbol of freedom & tranquility (or whatever), because blue is the color of the sky & the sky implies these qualities.