Theory: Quasi identicals appear similar for the following reasons:
An accepting dynamic perceiving function is more focused-seeming than the corresponding accepting static perceiving function, but the same static perceptive function is also more focused-seeming when it's a creative function than when it's accepting.
Also, a creative dynamic judging function seems less externally focused than an accepting dynamic judging function, but so does the corresponding accepting static judging function.
In addition, every function draws on its opposite (I/E) form to some extent.
Hence, quasi identicals appear similar.
Practice: Things that quasi-identicals do that are similar, and why they're different:
ISF: Enjoying a walk in nature.
ISFj: Focuses on identification with animals one passes by, and with the person one's walking with
ISFp: Focuses on losing oneself in "fun" things to do, telling stories, etc.
ESF: Acting like a wild person.
ESFp: Emphasis is on doing bold things
ESFj: Emphasis is on drumming up people's enthusiasm
EST: Taking charge.
ESTp: Emphasis is on being up at the front, doing things and achieving certain results
ESTj: Emphasis is on establishing order and cutting off inefficient activities
IST: Doing stuff very efficiently
ISTp: Emphasis is on personal action with a style of brevity or directness, and constant refinement of skill
ISTj: Emphasis is on keeping track of things in an orderly fashion and making sure they're being done a certain way
ENF: Enlisting people's support in a vision
ENFj: Assigns people roles, and determines how each person's actions fit into the overall picture; takes oversight of structure and delegates content creation; vision is likely to be somewhat well-defined, with lots of room for others to play prominent roles
ENFp: Announces a vision and seeks other people to play a support role and to give the vision structure; takes oversight of content creation and delegates structure; vision is likely to be rather open-ended, but with the ENFp playing the starring role
ENT: Creating a new endeavor or enterprise
ENTp: Talks about idea and begins realizing a prototype; plans to extend it or build it into something
ENTj: Gets busy creating a well-planned infrastructure; talks to people about it once it's in reasonable form; plans to effectively implement own enterprise, using hard work and well-conceived processes
INF: Discussing personal relationships
INFp: Is on a journey, constantly trying to figure out the meaning of one's life
INFj: Has clear personal choices one wants to realize, and enjoys discussing different possibilities for fun, stimulation, bonding with people, and acquiring necessary knowledge
INT: Discussing a philosophical theory or idea
INTp: Seeks to apply problem-solving abilities to problems, and put forth solutions to these problems, hoping for some sort of gain for oneself or others from one's various intellectual products and discoveries. Seeks to create methods and techniques that will aid in this process.
INTj: Seeks to extend and promote one's understanding of core reality and of the basic premises upon which to make sense or reality, and to build on this understanding and order one's actions accordingly in a fully consistent and well-ordered manner.
In addition to this, I hypothesize that in general, ability to tell quasi-identicals (and other similar types) apart is not completely symmetrical:
* N types usually value acting outside their normal personality more than S types
* Introverted types are more likely to not show their true behavior outwardly than extraverted types
* Irrational types are more inclined to change back and forth between personality roles than rational types
* T types are more likely to consciously experiment with their overall way of viewing the world than F types.
I'm interested in any additions to this...particularly examples of things that quasi-identity types or other similar but quadra-crossed types (contrary, comparative) do that look very similar, and why they're still different.