The process of contemplative practice (vipaśyanā-caryā) is the process of the equal cultivation of Samādhi and Prajñā

What is contemplation? Contemplation is the observation and examination of dharmas, followed by making a judgment and arriving at a conclusion. If this process is complete, it begins with the mind consciousness starting to contemplate, gradually deepening, with the mind becoming single-pointed and meditative concentration (samādhi) arising. Up to this point it is only a preliminary contemplation, relatively superficial and coarse. If a conclusion emerges, it is only the mind consciousness's coarse conclusion, not sufficiently refined; there is still doubt in the mind that has not been resolved—this is the doubt of the manas, meaning that the manas does not yet clearly understand or accept this conclusion. Contemplating further, the mind becomes increasingly single-pointed, meditative concentration grows ever deeper, the function performed by the mind consciousness becomes smaller and smaller, while the manas's contemplative and deliberative function grows greater and greater. Finally, when the manas's wisdom is sufficient to make a judgment, a conclusion that is true to reality and in accord with principle will be reached by the manas. Only then is doubt truly severed—this is the realization of dharma, the result of the mind consciousness and the manas cooperating in contemplation together.  

In contemplative practice (vipaśyanā-caryā) of the four foundations of mindfulness, one first cultivates the contemplation of the body as impure. To contemplate the body, one must first begin with the contemplation of breathing. The specific method of contemplation is all explained in the Buddhist sutras; as long as one honestly follows those contemplative steps one by one, one can observe the breathing and the condition of the body faculty as they truly are. For example, when you are now inhaling, know where the air enters from when you inhale; observe that the air enters through the nostrils, then passes through the nasal cavity into the lungs, and then into the dantian—this is roughly the process of inhaling. When exhaling, observe where the air travels from and to, where the air exits from, whether the breath is long or short, cold or warm, and what the body's sensations are—all must be clearly observed. When the mind is clear and lucid, one will know whether the breathing is deep or shallow, long or short, where the breath has traveled, where it is blocked and obstructed, and how the breath is exhaled. This is contemplation—the preliminary stage in which the mind consciousness plays the leading role.  

During the process of contemplation, when the mind is single-pointed, there is concentration, because all one's energy is focused on observing the breath, no longer attending to or pondering other matters. With no scattered thoughts in the mind, the mind settles into concentration. After attaining concentration, one must also maintain contemplation, keeping an inner awareness of the breathing. Regarding the dharma currently being contemplated, the mind must know it. If one cannot clearly know it, it indicates that the mind is scattered or has sunk into dullness. This knowing represents wisdom; with this knowing, the wisdom to eliminate self-view (ātma-dṛṣṭi) can gradually arise.  

Simultaneous with knowing, there is concentration; when the mind is very clear and lucid, there is wisdom—the equal cultivation of Samādhi and Prajñā, and the wisdom of emptiness will manifest. When contemplation reaches a certain degree, one can recognize that breathing is subject to arising and ceasing, impermanent, and that the body is subject to arising and ceasing, impermanent—wisdom then arises. This is the wisdom of the manas; the wisdom of the mind consciousness long ago knew that breathing and the body are impermanent, arising and ceasing—it knew this when studying the Dharma. But that knowing does not play a decisive role; only when contemplation reaches the end can the manas's knowing play the decisive role, and that is true wisdom. As long as the mind maintains this knowing, with prolonged practice and deepening effort, wisdom will arise, and one will be able to see the true reality of dharmas. This knowing, once the knowing of ignorance, becomes the knowing of enlightenment.