Let’s take the question closer to home. Let’s look at the breath, your breath. Sit with your breath. Deeply. Be with your breath, deeply. Where is the line that ­demarcates where your breath ends and where your body begins? Where is it within your body and the physiology of the oxygen penetrating ever deeper into the internal workings of your cells, its transformation into energy that then becomes a movement, a thought, and action that culminates with you picking up a bowl of food and ­offering it to nourish another person, who then proceeds to a clinic where you dispense medication for a sick child. What is the spatial conclusion of a breath? What does it not touch and connect with? Where does it cease in time? Where is the boundary line that distinguishes your body from external events, phenomena? The sound and your ear? The object directly in front of you, a certain color, and your eye? Where is the distinction that separates all that from the internal workings of your mind? From awareness itself? What is the boundary of reality that you’re experiencing right now? Is there a boundary of reality? How far does the light of the moon reach? How far does your mind and your eye reach in seeing the light of the moon? How does all of this rest in silence?

In the Foundations of Mindfulness, one of the basic teachings that Shakyamuni Buddha presented, he encourages us to look precisely at the nature of experience. Precisely and systematically. He is like Bodhidharma dispatching his student Huike to locate his mind so it can be put to rest. The four foundations of mindfulness are the body, accessed through the breath; feelings—basic attraction, repulsion and indifference; the mind; and the mind phenomena. Buddha is very thorough, and he guides us to be equally thorough. He invites us to find limits, to see where the boundaries are. What is the constant principle? Movement? Impermanence? What is that? What is that when there is just motion? Can motion be a constant? How? Where there is just impermanence, what is the nature of constancy?

Huineng delivers, “No, it’s not the flag. It’s not the wind. It’s your mind that’s moving.” Alarms should go off everywhere. Wumen immediately comes to the rescue. The first line in his commentary is, “It’s not the flag, it’s not the wind, it’s not the mind.” Don’t come to rest. Don’t hang onto Huineng’s brilliance. For an instant, it is the mind that moves. What is Huineng pointing to? Is he simply saying, “You two are just thinking?” Is he paraphrasing and acknowledging the fact that the three worlds are nothing but mind? The flag is the mind; the wind is the mind. Is there some esoteric teaching embedded here? When the mind moves, objects appear. With respect to what is the mind moving? You have to have a reference point for motion to happen. What is your mind moving against? What is it moving against when it is all of it? How do you resolve this koan?