There is actually a good definition for Chi, one which explains away all the mysticism. The problem is that intrinsic energy has been a catch basket for anything and everything that people didn’t understand. The truth is that Chi responds very well to simple physics definitions.
When one considers internal energy they must understand that there are several layers of it. These layers actually exist in stages, and they follow certain rules. To understand this consider that water is first ice, then water, then steam.
On the first level Chi is solid, it is the material which makes up bodies. That chair you are sitting in, it is made of frozen chi. So is the refrigerator and the TV.
On the second level, the one most people are most familiar with, intrinsic energy is a liquid like type of energy. Root your stance, move your body in a way that promotes generation and circulation, and you can feel the chi moving through your body. Interestingly, this chi actually moves through the solidity of your body.
The body is solid, but there are degrees of solid. Consider the body a stove, and the arms pipes, and it is easy to follow, and even create, the rules of how to move Chi energy. The real trick, of course, lies with understanding the third level of internal energy.
The third level of chi is thought, and this is the stuff by which you move the energetical substance through your body. Thought is interesting stuff, because people believe it is sentences and words and such. Thought, however, is not words, it is the urge behind the words.
What grunt of thought causes motion? What momentary impulse is behind all the sentences that try to describe internal energy in a thousand ways? What notion moves us, from bug to nation?
To move chi through the body one must learn to consider the universe on progressively lighter levels. One must move the objects of reality with muscle at first, and then progress to less effort and more intention, and finally enrich perceptions to the point where one can actually perceive the grunt or whim that actuates all motion in this universe. In the end, it is the effortless non-energy of perception that enables us to comprehend and understand chi, and to move it by whim and notion, and this effortless, light method is the secret of Tai Chi Chuan.