To rephrase that, consider the following request: "Look at your mind. You will see that it is empty." Notice anything odd about it? You're asking someone to "look" and yet you've preemptively decided what he's about to see! What if the student looks at his mind, sees that it's NOT "empty", and says so? Well, the conversation is over. The student obviously isn't "ready" yet, needs more practice, and so on and so forth until he does "see" this elusive "emptiness". It seems to me that a chain of expectations is being set up that forces the student to conceive a mental image of "emptiness" which, if the term hasn't been clearly defined, usually resembles what the student imagines "emptiness" to be like, and then "recognize" this apparition as the mind's "true nature". Refusing to describe what you're asking someone else to recognize doesn't even make sense unless you subscribe to the naive "you'll know it when you see it" school of lexical idealism, or the subject is impossible to describe in the established mode of communication. Guess which route many if not most modern students will take for granted: A shortcut offering the path of least resistance, or the sheer cliff face, climbing which it hurts even to contemplate? This isn't a danger to every practitioner of the Zen method, but it's certainly one of its greatest pitfalls. All methods, being methods, have these.
The mind is not physical. That's why it is empty.
As long as there is conceptualization, then it is not empty. What you are trying to do is grasping on to the mind like it is physical. We cannot get behind the mind until we become Buddha.
Now, some will no doubt accuse me of using "Western" thought processes to analyze an "Eastern" practice. So I'm wondering, will it come as a rude awakening when I report that I'm no "literal-minded Westerner"? What people forget is that Buddhism, unlike Taoism, did not originate in the Far East, but in my motherland and country of residence, India, where the lingua franca since ancient times was Sanskrit, not only an ancestor of my native tongue, but a cousin of Latin, Greek and great-uncle to, yes, English. A not so distant branch of the same cultural, intellectual and religious heritage that produced Pythagoreanism, Platonism and mature Christianity also gave form to the Buddhist tradition. I refer you to undeniable parallels in Apophatic Theology
to help alleviate your disbelief. It therefore remains to be established that Buddhism is so exotic that any trace of "Western" thinking is anathema to it. I know folks who will tell you all about how the characterization of systematic thought as "Western" is an offensive remnant of racism and colonialism. Just be thankful you'll not hear that lecture from me. Even if it were true that thinkers from different traditions can make no valid comments and criticisms about each other just because their norms are not 100% identical, a proposition I do not accept, I can only conclude that my would-be accusers are thoroughly deluded, given the embarrassing weight of evidence against their case.
By Western I mean Western philosophy which is based on sensual senses and the consciousnesses (in Buddhism, thinking is one of the consciousnesses). I am sure you have taken some courses. I have too.
So I would say experience through practice. This type of experience should not be based on emotional biases and biased thinking. This is a way of inquiring knowledge so to speak.