We can examine and analyze any object in depth to see what its essence is. We can probe until we get down to the level of atoms. Atoms can also be broken down until we come upon the indeterminate state of subatomic particles. Finally, if we try to go deeper still, there is nothing to observe. It is all happening in our imagination. There are no inherently existing, external objects, even though we firmly believe them to be solid, concrete, permanent, and strong. When you observe phenomena at a deeper level, all are seen to be hallucinations based in the mind. All that we see, feel, taste, smell, or hear is in relation to things, and if we examine any of these perceived objects carefully, we will not find any basis whereby we can establish true existence. We cannot find any substance in them; all are dissolving in place. For that reason, the great philosopher and meditation master Nagarjuna taught that whenever you perceive phenomena, there is actually nothing there.
One's current state of mind is similar to external objects in that it does not really have any kind of substantial existence to hold onto or grasp. A thorough inquiry reveals that there is no solid object called the mind. The mind is not located anywhere in time or space. It does not truly exist in an objective sense and is beyond conception. There is no exclusive or separate mind. Phenomena and noumena both seem to exist, but actually, there is nothing inherently real behind these appearances. Every subject and object is like the moon's reflection in water. All phenomena are of this illusory nature, free of self-existence and categorization within the four extremes of "being, nonbeing, both or neither." This is also known as the union of interdependent causation and emptiness.