Mindfulness, sati, is one of the nineteen sobhana cetasikas which have to arise with each sobhana citta. The Atthasdlini (I, Part IV, Chapter 1, 121) states that the characteristic of mindfulness is "not floating away'. Mindfulness "does not allow the floating away of moral states", such as the four applications of mindfulness and the other factors leading to enlightenment. Another characteristic of mindfulness the Atthasalini mentions is "acquiring" or "taking up" (1 In Pali: upaganhana.), that is, acquirement of what is useful and beneficial. Mindfulness, when it arises, "searches well the courses of states, advantageous and disadvantageous: -'these states are advantageous, those disadvantageous, these states are serviceable, those not serviceable'- and then removes the disadvantageous and takes up the advantageous."

     The Atthasalini then gives another definition of mindfulness:

... Mindfulness has "not floating away" as its characteristic, unforgetfulness as its function, guarding, or the state of facing the object, as its manifestation, firm remembrance (sanna) or application in mindfulness as regards the body, etc., as proximate cause. It should be regarded as a door-past from being firmly established in the object, and as a door-keeper from guarding the door of the senses.

     Mindfulness is non-forgetful of what is kusala and it keeps us from akusala. Also those who do not know about the Dhamma are able to perform wholesome deeds, but it is through the Dhamma that one can know more precisely what is kusala and what is akusala. Association with the good friend in Dhamma, listening to the Dhamma and considering it are most helpful conditions for mindfulness in the field of dana, sila, samatha and insight, thus, for all levels of mindfulness. The generosity, the patience and all the other good qualities of the true friend. in Dhamma can remind one to develop such qualities as well. 

     There are different ways of kusala and in order to be more heedful of what is wholesome, it is helpful to know more in detail about them. Dana, generosity, for example, is not only the giving away of useful things. There are also other ways of generosity included in dana, such as expressing our appreciation of someone else's kusala (anumodhana dana ). We may be stingy as to words of praise or we are lazy with regard to kusala and then we let opportunities for such a way of generosity go by. It is mindfulness which is non-forgetful of this way of generosity when the opportunity arises. Another form of generosity is to give someone else, no matter he lives in this world or in some other plane of existence, the opportunity to rejoice in our good deeds, so that he has kusala citta as well. It is rnindfuIness, not self, which is heedful of kusala. Without mindfulness it is impossible to perform any kind of kusala.

     Abstaining from ill deeds is a way of kusala included in sila. The Buddha explained in detail what is right and what is wrong. We should consider his words and test their meaning. Then we can verify ourselves the truth of his teachings. Before we studied the Dhamma we may not have known that also the killing of insects, for example, is akusala. Through the Dharnma we acquire more understanding of our different cittas, of kusala cittas and akusala cittas. We come to understand that killing is motivated by dosa and that the killing of any living being, insects included, is akusala kamma which can produce akusala yipaka. When we see the disadvantages of all kinds of akusala there are conditions for the arising of mindfulness which is heedful, non-forgetful of abstaining from akusala.

     Through the Dharnrna we learn about different ways of kusala. Before we studied the Dhamma we may not have-known that politeness and respect are ways of kusala kamma. Politeness and respect which are expressed by gestures or words are forms of sila. When there is an opportunity for such a way of kusala, mindfulness may arise and be non-forgetful of it, so that this opportunity is not wasted; that is the function of mindfulness.

     There is not only mindfulness which is non-forgetful of dana or of sila, there is also mindfulness with mental development. The development of calm,samatha,is one way of mental development. There is mindfulness with the kusala citta which develops calm. There are many degrees of calm. Jhana, absorption, is a high level of calm and it is extremely difficult to attain this level; one can only attain jhana if one has accumulations for it and if there is right understanding of its way of development. One may have no accumulations for jhana, but there can be moments of calm in daily life. For example, if there is right understanding of the characteristic of loving kindness, which is one of the meditation subjects of samatha, this quality can be developed in daily life and then there is calm conditioned by loving kindness. When there is calm, no matter of what degree, there is also mindfulness of the object of calm, be it loving kindness, compassion, the recollection of the Buddha or any other object of samatha.

     The study of the Dhamma is included in mental development. When we study the Dhamma with the aim to have more understanding of realities there is mindfulness at that moment. When we study the Dhamma and consider it there is intellectual understanding of realities and this is different from direct understanding of the reality which appears at the present moment. Intellectual understanding is a necessary foundation for the development of direct understanding or insight, vipassana. 

      In order to understand what mindfulness of vipassana is, we should know what its object is. The object of mindfulness in the development of vipassana is the nama or rupa which appears at the present moment. Nama and rupa are ultimate realities, different from "conventional realities" or concepts, such as person, mind, body, animal or tree. Concepts are objects we can think of but they are not real in the absolute sense.

     We should know the difference between ultimate realities and concepts. If we only know concepts and not ultimate realities we believe that a person or self really exists. We tend to think of a "whole" of mind and body, of the human person. When we study the Dhamma we learn that what we call mind are different types of citta accompanied by different cetasikas, and that these change all the time. What we call body are different rupas, some of which are produced by kamrna, some by citta, some by temperature and some by nutridon. These rupas arise and then fall away, they change all the time. Through the study of the Dhamma we leam about the different conditions for the cittas, cetasikas and rupas which arise. For instance, people are bom with different bodily features: some are beautiful, some are ugly, some are strong in body, some are weak. Such differences are caused by kamma. People have, as we say in conventional language, different characters, and through the Dhamma we acquire a more precise understanding of the conditions for their different characters. People had, in past lives, different abilities, different inclinations, and these have been accumulated from one moment of citta to the next moment of citta; therefore, they can condition the citta arising at the present moment. Kusala cittas and akusala cittas which arise are conditioned by accumulated inclinations to wholesomeness and unwholesomeness. We have pleasant experiences and unpleasant experiences through the senses and these are conditioned phenomena, they are yipakacittas produced by kamma. When we study the different conditions for the phenomena which arise we will understand more clearly that they are only fleeting phenomena, that there is no person or self who can exert control over the events of life.

     We are used to only paying attention to concepts, but through the study of the Dhamma we leam to see the value of developing understanding of ultimate realities, of nama and rupa. We learn through the study of the Abhidhamma that the sense-objects are experienced through their appropriate doorway by cittas which arise in processes. Visible object is experienced through the eye-door by cittas arising in the eye-door process. Tangible object such as hardness is experienced through the body-door by cittas arising in the body-door process. Each object is experienced through its appropriate doorway; tangible object, for example, could not be experienced through the eye-door. Only one object can be experienced at a time, through one doorway; the different doorways should not be confused with each other. When we only pay attention to concepts we think for example, that we can see and touch a flower. But in reality the seeing sees only what is visible, visible object, and the body-consciousness experiences tangible object such as hardness or softness. We can think of a 'whole" such as a flower because of remembrance of different experiences through different doorways. The thinking is conditioned by the seeing and other sense impressions.

     Nama and rupa appear one at a time and each one of them has its own characteristic. These characteristics cannot be changed. Seeing, for example, has its own characteristic; we can give it another name, but its characteristic cannot be changed. Seeing is always seeing for everybody, no matter an animal or any other living being sees. Concepts are only objects of thinking, they are not realities with their own characteristics, and thus they are not objects of which right understanding is to be developed. Nama and rupa which are real in the absolute sense are the objects of which right understanding should be developed.

    Only one reality at a time can be experienced by citta and thus also mindfulness which accompanies the kusala citta can experience only one object at a time. Since we are so used to paying attention to "wholes", to concepts such as people, cars or trees, we find it difficult to consider only one reality at a time. When we know the difference between the moments of thinking of concepts and the moments that only one reality at a time, such as sound or hardness appears, we will gradually have more understanding of what mindfulness is.

     In order to remind people of the truth of conditioned realities the Buddha taught about six doors, the objects experienced through these doorways and the realities which experience these objects. We read, for example, in the Middle Length Sayings (III, no. 148, "Discourse on the Six Sixes") that the Buddha, while he was staying near Savatthi, in the Jeta Grove, explained to the monks :

... When it is said. "Six internal sense-fields are to be understood", in reference to what is it said? It is in reference to the sense-field of eye, the sense-field of ear, the sense-field of nose, the sense-field of tongue, the sense-field of body, the sensefield of mind. When it is said, "Six internal sense-fields are to be understood" it is said in reference to this. This is the first Six.
     When it is said, "Six external sense-fields are to be understood". In reference to what is it said? It is in reference to the sense-field of material shapes, the sense-field of sounds. the sense-field of smells, the sense-field of tastes, the sense-field of touches, the sense-field of mental states. When it is said. "Six external sense-fields are to be understood", it is said in reference to this. This is the second Six.
     When it is said, "Six clones of consciousness are to be understood", in reference to what is it said? It is in reference to the visual consciousness that arises because of eye and material shapes; the auditory consciousness that arises because of ear and sounds; the olfactory consciousness that arises because of nose and smells; the gustatory consciousness that arises because tongue and tastes; the bodily consciousness that arises because of body and touches; the mental consciousness that arises because of mind and mental states.
     When it is said. "Six classes of consciousness are to be understood" it is said in reference to this. This is the third Six... 

     This sutta reminds us that each reality which appears through one of the six doors should be known separately, we should not confuse different realities with each other. We are so used to the idea of seeing people. However, the only object which can be seen is visible object. If there is mindfulness of visible object when it appears we will understand that visible object is a reality which can be experienced through the eyesense, that it is not a person. We may find it difficult to grasp this truth and we may wonder whether we have to avoid thinking of concepts. We do not have to avoid this, then we could not live our daily life. The citta which thinks of concepts is a reality, it arises because of conditions and it can be known as only a kind of nama, not self. We can live our daily life as usual, thinking of concepts and expressing ourselves by means of conventional language, in terms of "I", "self" or "person", but at the same time right understanding of nama and rupa can be developed. Even when we think of people and talk to them, there are nama and rupa which appear, and these can be objects of mindfulness.

     The cetasika sati, mindfulness, is different from what is meant by mindfulness in conventional language. Someone may think that he is mindful when he directs his attention to what he is doing or to what is going on around him. That is not the characteristic of sati in the development of insight. Sati of vipassana is, as we have seen, mindful of a nama or a rupa which appears, without there being a thought of self who makes a particular effort or who is directing the attention to an object. Also sati is only a type of nama, not self. 

     When there is mindfulness of a nama or rupa which appears, direct understanding of that reality can at that moment be developed. When we learn a subject such as mathematics or history, we study books and try to understand the subject we study. In order to understand realities we have to investigate or "study" them, but that is not study through thinking, it is the development of direct understanding of realities. When a reality such as sound appears and there is mindfulness of it, its characteristic can be "studied" or investigated, just for an extremely short moment. In that way it can be known as it is: a conditioned reality which does not belong to anyone. The word "study" can remind us that there should be mindfulness of realities again and again, until they are known as they are. Full understanding cannot be achieved within a short time.

     As we have seen in the definition of the Atthasalini, "guarding" is a manifestation of mindfulness. Through mindfulness the six doors are guarded. When there is no mindfulness after having seen visible object through the eyes, there is bound to be attachment, aversion and ignorance on account of the object. We are absorbed in the objects which are experienced through the six doors. When mindfulness arises there is no akusala citta on account of the object which is experienced and thus the doorways are guarded. The Atthasalini compares mindfulness with a doorkeeper.       In order to understand the function of mindfulness it is helpful to know the danger of the absence of mindfulness. The definition of "Heedlessness" in the Book of Analysis (Vibhanga, Chapter 17, Analysis of Small Items,  846) reminds us of the danger of akusala and the value of mindfulness which guards the six doors. We read: 

      Therein what is "heedlessness'? Wrong bodily action or wrong verbal action or wrong mental action or the succumbing and repeated succumbing of consciousness to the five strands of sense pleasures or not working carefully, not working constantly. working spasmodically. Being stagnant, relinquishing wish (desire-to-do, chanda), relinquishing the task non-pursuance, non-development, non-repetition, non-resolution, nonpractising, heedlessness in the development of good states; that which is similar, heedlessness, being heedless. state of being heedless. This is called heedlessness. 

     It may seem uninteresting to investigate realities such as visible object, seeing, sound or hearing, but we should remember that right understanding of realities bears directly on our daily life. It can eliminate wrong bodily action, wrong verbal action and wrong mental action. When wrong view has been eradicated completely we shall never again neglect the five precepts since there are no more conditions for neglecting them. Even when one has not yet become a sotapanna, mindfulness can prevent akusala kamma. For instance, when there is an unpleasant sound aversion may arise and it could motivate akusala kamma. Whereas when there is mindfulness of sound as only a kind of rupa, not the voice of someone, not the sound of a radio, the doors are guarded. When mindfulness guards the six doors it is to the benefit of ourselves as well as of other people.

     As we have seen, the Atthasalini states that the proximate cause of mindfulness is ill remembrance (sanna) or the four applications of mindfulness (satipatthana). There can be mindfulness of the nama or rupa which appears because of firm remembrance of all we learnt from the teachings about nama and rupa. Listening is mentioned in the scriptures as a most important condition for the attainment of enlightenment, because when we listen time and again, there can be firm remenbrance of the Dhamma. Mindfulness is different from remembrance, sanna. Sanna accompanies every citta; it recognizes the object and "marks" it, so that it can be recognized again. Mindfulness, sati, is not forgethe of what is wholesome. It arises with sobhana cittas. But when there is sati which is non-forgetfuI of dana, sila, of the object of calm or, in the case of vipassana, of the nama and rupa appearing at the present moment, there is also kusala sanna which remembers the object in the fight way, in the wholesome way.

     The other proximate cause of mindfulness is the four applications of mindfulness or satipatthana (1 satipatthana means mindfulness of vipassana or the object of mindfulness of vipassana.) . All realities can be object of mindfulness in the development of insight and are thus included in the four applications of mindfulness which are rupa, feeling, citta and dhamma. For those who have accumulations to develop calm to the degree of jhana and to develop insight as well, also jhanacitta can be object of mindfulness in vipassana, in order to see it as non-self. Right understanding of realities is developed through mindfulness of any nama or rupa which appears now, be it akusala citta, maha-kusala citta, jhanacitta or any other reality. One should not try to direct mindfulness to a particular object; there is no self who can have power over any reality or who can direct sad. There is not any reality which is excluded from the four applications of mindfulness.

     Mindfulness is one of the "five spiritual faculties" (indriyas) Which should be developed. As we have seen, the other spiritual faculties are: confidence, energy, concentration and wisdom. We read in the Dhammasangani (14) about the faculty of mindfulness:

What on that occasion is the faculty of mindfulness?
     The mindfulness which on that occasion is recollecting, calling back to mind: the mindfulness which is remembering, bearing in mind, the apposite of superficiality and of obliviousness; mindfulness as faculty (indriya), mindfulness as power (bala), right mindfulness- this is the faculty of mindfulness that there then is.

... "non-superficiality" (in the sense of diving or entering into the object) is the state of not letting the object float away. Not as pumpkins and pots, etc., which float on the water and do not sink therein, does mindfulness sink into the object. Hence it is said to be non-superficiality... .

... It exercises government (over associated states) in the characteristic of presenting or illuminating the object- this is the faculty of mindfulness.

... It does not fluctuate on account of negligence- this is "strength of mindfulness " Right mindfulness " is irreversible, emancipating, moral mindfulness.

     Right mindfulness is one of the factors of the eightfold Path. It is "emancipating"; the factors of the eightfold Path lead to freedom from defilements. Mindfulness is alto one of the enlightenment factors (bojjhangas). The other factors are: investigation of Dhamma (dhamma vicaya), energy, enthusiasm (piti), tranquillity (passaddhi), concentration and equanimity.

     One may wonder how, in the development of insight, the faculty of mindfulness, the power of mindfulness, the Path factor right mindfulness and the enlightenment factor of mindfulness can be developed. The answer is: through mindfulness of the nama and rupa which appears right now. There is no other way. Sights, sounds, scents, flavours and tangible objects are most of the time objects of attachment, aversion and ignorance. If mindfulness arises and right understanding of the object is being developed, one is at that moment not enslaved to the object nor disturbed by it. If we understand that mindfulness of realities can eventually have an immediate effect on our daily life, we will have more courage to develop it at this moment.