A few days ago I had a passing idea that the inferior function's opposite is the theoretic last preferred/least developed function. Since, the concept has grown slightly in scope.
The implications are as follows:
ENTP - Ne/Ni/Ti/Te/Fe/Fi/Si/Se
ISTP - Ti/Te/Se/Si/Ni/Ne/Fe/Fi
INFJ - Ni/Ne/Fe/Fi/Ti/Te/Se/Si
ESFJ - Fe/Fi/Si/Se/Ne/Ni/Ti/Te
If drawn out proper, it would look a little something like this:
The secondary function set is perhaps actuated by extenuating circumstance, such as stress at work or being placed in an unfamiliar/uncomfortable situation. I know in my case when under stress, I become less of a Ti user and more of a Te user, but not an inefficient Te user... also in line with my thinking is that I am highly insusceptible to displaying Fi, perhaps making it my last theoretical preferred function.
An example of external thinking would be an ENTP undergoing relationship troubles, attempting to Ni signs out of every gleaning spot of information available. It is not a preferred modus operandi, but exists nonetheless.
I suppose, if you'd like to weigh in, consider the opposites of your dominant through inferior functions and how/when you actually use them, presuming you do. Can you relate at all to this? Are you aware of theory already in this vein? I've heard Socionics has an opinion of shadow functions similar to mine.
Anyways, this is just fun, self-indulgent thinking for me, any critique encouraged.