Whatever sorts of thoughts arise, without suppressing them, recognize what they emerge from and what they dissolve into; and stay focused while you observe their nature. By doing so, eventually, the motion of thoughts ceases, and there is stillness... each time you observe the nature of thoughts that arise, they will vanish by themselves following which, a vacuity appears. Likewise, if you also examine the mind when it remains without movement, you will see an unobscured, clear and vivid vacuity, without any difference between the former and latter states. That is well known among meditators and is called “the union of stillness and motion.”