When I first tried to tackle understanding all the functions, I noticed that "objective" and "subjective" were sometimes used to describe both the functions themselves, and where they were used. I was trying specifically to understand how they shaped directing and informing communications in the eight three letter groups (STJ, SFP, etc) that Keirsey had identified. So I paralleled things up along the line of subjective and objective. (I had thought that "directing" communications, such as S and T together might have had to do with "objectivity". Turned out it might work to some extent for judging functions, but it seems for perception it is the opposite).
Thinking is generally condsidered "objective", based on logic and facts, while Feeling is considered subjective "values".
"extraverted attitudes" (outside use) is also considered "objective", while introverted attitudes are considered subjective, because they are taking place within the person. (For perception, the attitude is the "source" it is taken from, and for judgment, it is the "realm" it is used in).
Sensing (concrete perception) is also considered more "objective", while iNtuiting (abstract) is considered subjective, because it involves the person drawing from patterns and stuff.
I then tried to shorthand the processes with "o" for "objective" and "u" for "subjective".
Se objective data from objective source O/O
Si objective data from subjective source O/U
Ne subjective data from objective source U/O
Ni subjective data from subjective source U/U
Te objective judgment in objective realm o/o
Ti objective judgment in subjective realm o/u
Fe subjective judgment in objective realm u/o
Fi subjective judgment in subjective realm u/u
So these can be put together for an alternate code for the 16 types. The case is used to distinguish perception and judgment, and which order they are placed in would determine the dom/aux function and attitude.
(One person said, in essence; "what, more letter codes?" and I basically dropped the idea).