Letting Intent Surface

"Chen Style Taijiquan: The Source of Taiji Boxing" has the following description of how Xin (mind) and Yi (intent) are harmonized:
"One must quiet and relax the mind. When the mind is calm Yi (intent) surfaces. One can then concentrate and focus the Yi" (D. Sim & D. Gaffney, pg 69)
It is a good reminder that what you don't do is very important in the internal arts. Overthink and you will not get anywhere. Still the mind and opportunities will follow.
The book the above quote comes from provides an excellent overview of central Taiji training concepts. It smartly avoids trying to teach the forms and focusses on being a resource for students. Certainly one of the better books on Taijiquan in English.

Experiencing Qi

Qi is not as mysterious or esoteric as many make it out to be. To be alive means that Qi is active and moving within our bodies. Like a magnet that has a North pole, a South pole and the lines of force that are created as a result, in living beings, consciousness being present in the body creates the flow of Qi.
What makes Qi so elusive is the fact that it is always present – we experience Qi like a fish experiences water.

The 3 Internal Harmonies

Chen Zhenglei, details the 3 internal harmonies as Shen (mind) with Yi (intent), Qi with Li (strength) and tendons with bones ("Chen Style Taijiqian, Sword & Broadsword" pg. 96). This differs from other versions but the fact that he is a scholar as well lineage bearer make me believe that this is more than just an idiosyncratic interpretation.
Missing is the harmony of qi and yi. However it is often said that "Qi follows Yi" automatically. The addition of tendons and bones is interesting to me because of what I know of Magui style Bagua. Tendons & Bones are extensions of the Liver & Kidney networks, the two deepest in the body. Magui bagua's approach is to train Qi & Blood primarily. This is required to build up the tendons (and, I think, bones). To train more externally, working say the muscles, might appear to be quicker, but the gains are temporary and increases the risks of injury. Staying focused on training Qi & blood builds the body from the inside out.
Chen Zhenglei's inclusion of the tendons & bones, I think reflects similar thinking. The structure (bones and tendons) need to be harmonized, not forced or worked. This allows the proper opening of the body and the full circulation of Qi throughout all of the channels and networks. This pair is also provides a linkage to the 3 external harmonies (which describe the requirements of proper posture & alignment), making the 6 harmonies more integrated.