I'm not in any way arguing that it is an objective standard. My questioning is whether or not it holds up as an approximate/subjective standard. There are different vantage points from which to view subjective systems. The personal bias viewpoint is one that has a degree of use, but my point is that it is not the only position from which to view such a system. Just like taste in music has meaning based only on personal bias, but there are other vantage points from which to evaluate quality and meaning on a larger scale.
I am debating that since MBTI is a system that overlays and makes sense of the larger scale, it needs to demonstrate some kind of approximate mapping to relating on the same scale it is attempting to address as a system. If people take away from it only their own type description and internalize it, that is one thing, but when they project its meaning onto to others as having any validity, it needs to demonstrate validity outside the context of self. When people project types onto people who when tested do not consistently report a type, their premise is flawed. The poles created by the system are not demonstrated to be mutually exclusive in a way that people in general can identify with a category.
Subjective systems have relative accuracy. The way to approach these is to extract the underlying principle which can be measured and observed. It is the elaborations on the principle within a specific context that are subjective. Edit: This is because the influences are too numerous to account for in a practical manner, or are by nature difficult to observe or measure, and therefore create an approximate or subjective system. /edit. To use a metaphor: the principle behind how a crystal forms would produce a perfect geometrical shape. In reality the crystal forms from a combination of this underlying principle and the effects of gravity, erosion, etc. to form an object that is somewhere between perfectly structured and influenced by layered forces.
The principle of human beauty is subjective. Some people approach it as strictly based on personal bias. The underlying principle is that evidence of genetic and physical health are preferred. This is the core, it has some capacity to be observed and measured. In its specific application the layers of individual psychology and cultural ideals overlays specific ways the principle is elaborated upon to form distinct and often contrasting ideals of beauty.
Human psychology has core elements that can be measured. Human brains are structured similarly. There are underlying principles upon which contextualized elaboration occurs. The core principles can be measured. If they cannot be observed and demonstrated in some manner, then perhaps it has not been properly identified.
If a subjective system in going to having meaning outside the context of the individual, or a group of individuals, then yes, it does have to demonstrate a core principle that can be identified, observed,and measured.
It always surprises me how people assume that subjectivity is equivalent to free reign of personal bias. The assumption appears to be that because something is subjective it can in no way be measured or placed against an external standard. I am trying to keep the thread on topic, but have to wonder if the lack of arts education is resulting in this complete lack of being able to relate to approximate information in any way other than individual perspective. This post is probably too long for anyone to bother reading, but i hope some of the principles are laid out clearly enough. Understanding that way of disregarding everything except self when dealing with something subjective explains most of the misapplications of MBTI and even the way people readily adopt systems that might have problems in their design. Rejecting any external reference does pretty much leave someone to their prejudices and little else.