I've read that the two can somehow be used in Unison, with benefit. Can anyone expand on this?
Anapanasati is divided into 4 tetrads which correspond to the 4 Satipatthana hence the pratice of Anapanasati is actually a forms of Satipatthana / Vipassana. A thorough introduction to Anapanasati and how to develop this into Vipassana is difficult in this format hence it might be worthwhile to read a more elaborate book on it: Anapanasati: Mindfulness of Breathing by Buddhadasa Bhikkhu. You can complement this book with: Right Mindfulness: Memory & Ardency on the Buddhist Path by Thanissaro Bhikkhu
In this post I will touch on one aspect of the Vipassana side to Anapanasati meditation - Contemplation of Mind Objects. Contemplating on Impermanence, He Trains (as part of Anapanasati Meditation) “Contemplating impermanence, he breathes in. Contemplating impermanence, he breathes out. Thus, he trains himself.” Anicca means ‘impermanence’. Being able to see everything in terms of impermanence is not something that comes automatically after gaining concentration of mind. Now, he trains himself to breathe in contemplating impermanence, and he trains himself to breathe out contemplating impermanence.
Some meditation teachers declare that impermanence is something that just becomes visible to a mind, like appearing in a meter, and enables one to gain something called ‘vipassana nana’ (insight knowledge) by continuous determination. This theory or view is not in accordance with the Supreme Buddha’s Dhamma.
Impermanence of Breath
Anapanasati is something that should be developed and pursued mindfully and discerningly. Now, he trains himself to breathe in focusing on impermanence, and to breathe out focusing on impermanence. Purity of mind has been achieved through the elimination of the hindrances (nivarana). His effort, mindfulness and concentration are now being directed towards focusing on impermanence. He is contemplating on impermanence within anapanasati. He can see the impermanent nature of his own breath in its rise and fall; the impermanence of his body; and the impermanent nature of the pleasant feeling and perception that he experienced.
Impermanence of Body
What has he seen in the body? What does this body consist of? This physical body contains and comprises the four great elements, which are known as: solidity/earth (pathavi), fluidity/water (apo), heat or temperature (tejo) and air (vayo). We generally use the word rupa (material form) to denote the body. When he is breathing in and out, he is focusing on impermanence of material form which is derived from the four great elements.
Impermanence of Feeling
Thereafter, he is focusing on feelings. Dependent on contact, feeling arises. What is contact? Contact is the coming together of three things. For example, eye, form and eye-consciousness come together, and it is their convergence, that is called contact. Similarly, with ear and sounds, nose and smells, and so on, through to mind and mental-objects.
In this instance, when body, tangible object and consciousness come together, there arises contact. With the arising of contact, simultaneously, there arises feeling (vedana) – feeling born of body contact. Since feeling is conditioned by contact, feeling differs in accordance with the change of contact. This way, he contemplates on the impermanence of feeling.
Impermanence of Perception
Then, there is the recognition of perception. This is called sañña (perception) which is also subject to change as it is conditioned by contact. Perception changes due to impermanence of contact.
Impermanence of Formations
Perception is followed by sankhara (mental formations). If the mental factor was directed to a certain matter, on that occasion there is volitional activity, and this is called sankhara. Here, he observes the impermanence of the mental formation with the change of contact. All these are based on the activities of the mind.
Now he understands every aspect in this life process which was considered as self (form, feeling, perception and formation); or anything pertaining to a self. He has real wisdom to see things as they really are. One may contemplate on impermanence saying “anicca, anicca” continuously, but still be holding onto the notion of “I am” or “mine”. To avoid this, it is important to realize the impermanent, no-self nature in inhalation-exhalation and in any other external object.
Impermanence of Consciousness
Finally, he sees the impermanent nature of all that has been cognized (the rise and fall of breath, rapture, joy, feelings, and perceptions). It is through this insight that the true nature of the five aggregates of clinging is understood and seen in the light of impermanence:
material form (rupa) derived from the four great elements, feeling (vedana) that is conditioned by contact, perception (sañña) that is conditioned by contact, mental formations (sankhara) that is conditioned by contact, and consciousness (viññana) that is conditioned by mentality-materiality (nama-rupa)
Being fully concentrated on anapanasati, he now dwells ardent, with full awareness, and clear comprehension of impermanence. With the base of this awareness, established in anicca (impermanence), he develops an understanding of his own life, the impermanent nature of others who breathe and live, and the impermanent nature of material form, feeling, perception, mental formations and consciousness (the five aggregates of clinging).
Thus, he observes the impermanent characteristic of phenomenal existence, internally and externally. He does not see a difference in him and the outer world. He sees the characteristic of phenomenal existence as subject to cause and effect. Now he is gaining knowledge, and his comprehension is increasing. He sees things as they really are, in whatever material form: whether past, present or future, far or near, external or internal. He sees the impermanence even of the rapture and pleasure that he is experiencing in breathing mindfully. Now, based on the impermanent breath, he understands the impermanent nature of the five aggregates of clinging.
He realizes that whatever is impermanent and subject to change, is suffering (dukkha). And, whatever is impermanent is without self (anatta). It is through this insight that the true nature of the aggregates is clearly seen; in the light of three signs (ti-lakkhana): impermanence (anicca), suffering (dukkha) and without self (anatta).
He sees the impermanent, suffering and no-self nature of all conditioned and component things. As a result, he knows there is no “I”, no self, or anything pertaining to a self. When he trains himself to breathe in and out focusing on impermanence, he understands that anything taken as ‘mine’ is impermanent; anything taken as ‘I am’ is impermanent; and anything that is taken as ‘my self’ is impermanent. He realizes that whatever is impermanent, is without self. That which is without self, is not ‘mine’, not ‘I am’, and is not ‘my self’. Thus he sees everything as it really is – with wisdom.