Samādhi means concentration, one-pointedness of mind. When one fixes one’s mind on any object, it is called samādhi i.e., concentration of mind. Concentration may be right (sammā samādhi) or wrong (micchā samādhi). When a cat concentrates its mind to catch a rat or a stork stands on one leg on the bank of a pond to catch fish, it is called concentration of akusala citta (unwholesome mind). Such mind can cause only destruction. But the samādhi that does one good is really the concentration of wholesome mind which is called sammā samādhi (kusalacittassa ekaggatā samādhi). This kind of samādhi is very helpful for a person who wants to make progress on the spiritual path.
The characteristic (lakkhaṇa) of concentration is unwavering, undistracted. In other words, its characteristic is one-pointedness. Its function (rasa) is to remove distraction. It manifests itself as being non-wavering and bliss is its immediate cause. Concentration makes mind stable, unwavering and undistracted.
Mind is naturally very fickle and unsteady as it keeps on wavering and getting distracted. But once it is tamed and controlled, it has infinite power to do good. One can make good use of it and make it capable of doing wholesome work. That is why it is said in the Dhammapada that a well-directed mind (sammā panihitaṃ cittaṃ) is far more helpful than even one’s parents. In other words, what one’s parents cannot do, one’s mind can do for one.
‘Na taṃ mātā pitā kayirā, aṭññe vā pi ca ñātakā/
Sammā panihitaṃ cittaṃ, seyyaso naṃ tato kare//’
Similarly, if the mind is not controlled and tamed then it can do a lot of harm, it can do greater harm than even one’s enemies can do.
‘Diso disaṃ yaṃ taṃ kayirā, verī vā pana verinaṃ/
Micchāpanihitaṃ cittaṃ, pāpiyo na tato kare//’
One can direct one’s mind only when one has control over it. For this, practicing meditation is necessary.
Meditation cannot be practiced unless the impediments are removed. In the Visuddhimaggo, Buddhaghosa has enumerated ten impediments. They are: a dwelling place (hut, room or monastery where many things are stored which will distract his attention), family (relatives or supporters who will often visit him and take his time), gain (it is an impediment in the sense that when a bhikkhu gets requisites, he has to teach the givers, thus not getting time to do his duties), class (if he has to teach suttas or Abhidhamma to students, he hardly finds time to meditate), nava-kamma (building work or repair work also takes a lot of time), travel (if he has to undertake a journey, he will keep thinking about it and will not find time to meditate), kins (either mother, father or other relative or one’s teacher, co-resident, pupil etc. who will take his time,), illness (a great obstacle, because if he is ill he cannot undertake the arduous task of doing meditation), books (if he is busy reciting them, they will prove distracting) and supernormal powers (great impediment for attaining insight, these powers are obtainable through meditation, but meditation should not be a means for attaining supernormal powers but it should be a means to attain insight).
But these are very gross obstacles which are visible, but there are many subtle impediments called defilements such as kāmachhanda (sensuous desire), vyāpada (ill-will), thinamiddha (sloth and torpor), uddhaccakukucca (restlessness and scruples) and vicikicchā (doubt). They are great distracting forces.
For being able to practice meditation, one has to observe moral precepts. By observing moral precepts, one tries to minimize or drive out different defilements from mind. It is these defilements which distract the mind and do not let it concentrate. By observing sīla (morality), one keeps his physical and vocal actions pure. This means that he is able to keep greed, ill-will, sexual desire, fear etc. at bay which will not prompt him to do unwholesome and impure physical and vocal actions.
Besides observing moral precepts, one has to ask for a suitable kammaṭṭhāna (meditation subject) from one's teacher who is called a kalyāṇamitta.
There are several kammaṭṭhānas. Buddhaghosa enumerated forty of them, such as ten kasiṇas, ten kinds of asubha (foulness), ten recollections such as buddhānussati, four brahmavihārā such as mettā, karuṇā etc.
These kammaṭṭhānas are not suitable for all; what is suitable for one may not be suitable for another person. The reason for this is that there are different types of people with different temperaments. Some are greedy (rāga carita), some are hateful (dosa carita), some are deluded (moha carita), some are faithful (saddhā carita), some are intelligent (buddhi carita) and some are speculative (vitakka carita).
Ten kinds of foulness (asubha) that one observes in the cemetery such as a bloated, discolored and festering body being eaten by crows and vultures and the observation of the thirty-two parts of body (atthi imasmi kāye kesa, lomā, nakhā, dantā etc.) are the suitable meditation subjects for greedy and lustful people. They have excessive sense-desire. They are very much enamored with physical beauty. When they observe the impurities that the body contains and what happens to it after one is dead, they become disillusioned and gradually get rid of attachment to it.
The four brahmavihārā and four color kasiṇas are suitable for one with a hateful temperament.
Mindfulness of the incoming and outgoing breath is a suitable meditation subject for persons of a deluded temperament. It is also suitable for people of a speculative temperament.
Out of the ten anussatis, the first six such as buddhānussati, dhammānussati etc. are suitable meditation subjects for the people of the faithful temperament.
Mindfulness of death, the recollection of peace, the defining of four elements such as paṭhavī (earth), āpo (water), tejo (fire) and vāyo (air) and the perception of repulsiveness in nutriment (āhārepaṭikkūla saññā) are suitable meditation subjects for people of an intelligent temperament.
The rest of the meditation subjects, kasiṇas and immaterial states are by and large suitable for all people.
A concentrated mind leads to absorption. When one meditates on some visible object suitable to one’s temperament, one becomes so absorbed in it that all other thoughts are driven out of one’s mind. It means that the mind is absolutely concentrated on that object, so much so that that a stage comes when one can visualize the object even when one’s eyes are closed. One concentrates the mind on this visualized image called uggaha nimitta then makes further progress in attaining concentration of mind. This enables one to develop uggaha nimitta into paṭibhāga nimitta (conceptualized image).
One makes further progress in developing the concentration of mind and thus possesses what is called upacara samādhi (proximate concentration). Upacara samadhi means that one is very near to attaining appanā samādhi (ecstatic concentration). When one is at this stage, the five hindrances mentioned above are kept firmly at bay, although only for as long as one is at that stage. This is called rūpāvacara jhāna (fine material absorption). There are five factors of rūpāvacara jhāna. They are vitakka (initial application), vicāra (sustained application), pīti (joy), sukha (happiness) and ekaggatā (one-pointedness). In the second rūpāvacara jhāna, vitakka is dropped; in the third, vicāra is dropped, in the fourth, pīti is dropped; in the fifth, sukha is dropped and is replaced by upekkhā in the sixth fine material absorption.
After one has attained mastery over fine material absorption, one develops absorption more and more and then attains the four formless concentrations. They are Ākāsanañcāyatana (one concentrates thinking that space is infinite), Viññāṇāñcāyatana (one concentrates thinking that consciousness is infinite), Ākiñcāññāyatana (one concentrates thinking that there is nothing) and Nevasaññānāsaññāyatana (one concentrates thinking that there is neither perception nor perceiver).
The last is the highest state of absorption, the highest of the samatha (calm) type of samādhi. But in the samatha type of samādhi, one controls only the paritta citta (small part of the mind or conscious mind). If one attains this absorption, one will have full control over the sense organs and will not create any new saṅkhāras (navaṃ natthi sambhavaṃ) but one will not be able to observe and control the subconscious and unconscious parts of mind where every moment taṇhā (desire) is being created without one being aware of it.
The Buddha discovered vipassana meditation practicing which one can be aware of what is happening within, where craving is being created and how this process of entangling one in infinite misery can be stopped. Here, besides attaining concentration of mind, sati (mindfulness) and sampajañña (knowledge of anicca, dukkha and anattā at the experiential level is gained) are developed. Ultimately, this realization leads one to develop non-attachment to the objects of the world, craving for which keeps one moving in the cycle of birth and death, suffering birth after birth endlessly.
Samādhi is actually samatha–concentration of mind, but vipassana is to experience anicca, dukkha and anattā and to develop nirveda.
Forty kammaṭṭhānas called ārammaṇas are the subjects of meditation suitable for practicing samatha type of meditation. So, they are called ārammaṇūpajjhāna. For practicing vipassana, lakkhaṇas such as anicca (impermanence), dukkha (suffering) and anattā (no-self) of an object are suitable subjects of meditation. These three, therefore, are called lakkhaṇūpajjhāna.
In short, concentration of mind can be achieved by one who observes the five moral precepts, removes defilements from one’s mind and focuses the mind on one of the forty kammaṭṭhānas (subjects of meditation). Vipassana, however, can be practiced when such a person realizes the three characteristics of all objects of the world i.e., anicca, dukkha and anattā.