Fred Little wrote:
Perhaps I missed it, but I have yet to see a post that has an "accurate description" that is expressed in plain english and provides an objective basis for the identification and evaluation of "jin" along empirical rationalist lines of the kind you continually press.
It's really no more than you've asked of anyone else.
If you could point all of us to a post in which you have already answered the question, that would be a big help.
I damned if I do and damned if I don't on this one... either I take the time to write it out or I go search the archives for things I know that I've already written!
"Jin" is the pinyin for the word which originally has become part of the New Age culture because it was translated as "Energy". Hence you read a lot of stuff about "the ward-off energy", etc., in many Taiji books, "feel the energy", etc. However, that word "energy" was decided upon by a number of earlier translators, none of whom had any real martial skills, and it turns out to have been seriously misleading.
A more accurate definition from the choices available would have been a translation implying that "jin" is a trained-force-skill with perhaps a hint of "force vector" in it. When you use "jin" you use a strength skill which has been developed through practice, as opposed to "brute strength". Since the main "jin" that is chronicled in Chinese martial-arts-related articles is the "jin from the ground, controlled by the waist, manifested in the hands", it also has a close relationship to the idea of qi/ki and strength, which are always related. So it's really impossible to have a "jin" which is not an expression of "qi/ki" and a lot of confusion ensues. Tohei showing his "ki" is actually demonstrating his "jin" or his "kokyu ryoku". Often if you re-read an translated article and insert the words "strength-skill-controlled by the mind" for 'qi/ki', you can suddenly see the pragmatics involved in a heretofore mystical-sounding passage.
Under the umbrella-term/paradigm of "qi/ki" is also the idea of qi/ki being a part of the connective-tissue functions of the body. For instance, some Chinese used to postulate that an "iron shirt" (trained method of becoming resistant to blows, etc.) worked because the qi in the connective-tissue rose to meet any incoming blow. The idea of the connective-tissue, tendons, etc., being associated with qi goes back to the Yellow Emperor classic (i.e., this stuff has been around a long, long time). Because the connective-tissue can be trained by manipulating the breath and pressures/tensions in the body and because this enhanced conditioning also adds greatly to your strength, it naturally enhances your "jin" power. So "breath" in conjunction with well-developed "jin" is indeed "breath power". In fact this association of breath and jin is completely standard and common... the Japanese choice of the term "kokyu" is blatantly understandable in this light.
A caution should be made that "jin" is also the pinyin spelling for a different word (a different tone is used in the pronunciation) meaning "semen" or "sexual essence"... and a lot of people reading about "jin" and "qi" need to decide which of these meanings actually applies to what they're reading. Don't forget that the ultimate goal of most meditations is to literally raise "semen" or "sexual essence" up the spine (hey, the idea comes from India) and into the cranial cavity called the "shen" (shin in Japanese). Thence comes "enlightenment".
That's a thumbnail sketch, Fred. I could expand on something if there's a question.