For my brothers, sisters, friends and beloved enemies: You are a yang creature, from the moment you were born until the moment you die, you will always be yang. By your living, fiery yang nature, it is impossible to sense yin directly in the same way it is impossible for the spirits to generate yang unaided. This natural duality is what separates the living from the dead, life from death. That is all. Concerning what is called "Yin": When the novice begins cultivation, they follow their nature and cultivate yang FIRST. However, after a certain period practice - perhaps several months or a few years, they will detect the presence of "another" energy hovering near their yang ball. This will feel like some kind of magnetic repelling force, quite distinct from the boiling hot (and painful) yang energy they have built up. It is almost identical to the sensation you feel when pushing two repelling magnets together. This is yin. Yang flows through yin. By its nature, yang tends to concentrate into a single point when isolated - but in the presence of yin, it diffuses and flows freely. When these two forces are working harmoniously, they generate a sensation similar to an electrical current. Detecting yin: As mentioned before, it is impossible to directly detect yin simply because of how you are wired. In fact, even my descriptions give an indication of my yang nature - that I use the yang I've cultivated to map out the boundaries and rigidity of the yin field. It is in this exact fashion that you can detect the presence of yin - yang will naturally react to its presence. When a common spirit is nearby, which will certainly be yin in nature, watch for sensations of an electric prick or disturbance in your yang. This will occur in your extremities, 3rd eye, or even lower dan tian if you have sufficient energy and if the spirit is strong enough. I hope this helps for now , please meditate -sitting on the earth- and everything will become clear to you.