The eighth factor of the path is right concentration, in Pali samma samadhi. Concentration represents an intensification of a mental factor present in every state of consciousness. This factor, one-pointedness of mind (citt'ekaggata), has the function of unifying the other mental factors in the task of cognition. It is the factor responsible for the individuating aspect of consciousness, ensuring that every citta or act of mind remains centred on its object. At any given moment the mind must be cognizant of something -- a sight, a sound, a smell, a taste, a touch, or a mental object. The factor of one-pointedness unifies the mind and its other concomitants in the task of cognizing the object, while it simultaneously exercises the function of centring all the constituents of the cognitive act on the object. One-pointedness of mind explains the fact that in any act of consciousness there is a central point of focus, towards which the entire objective datum points from its outer peripheries to its inner nucleus.
However, samadhi is only a particular kind of one-pointedness; it is not equivalent to one-pointedness in its entirety. A gourmet sitting down to a meal, an assassin about to slay his victim, a soldier on the battlefield -- these all act with a concentrated mind, but their concentration cannot be characterized as samadhi. Samadhi is exclusively wholesome one-pointedness, the concentration in a wholesome state of mind. Even then its range is still narrower: it does not signify every form of wholesome concentration, but only the intensified concentration that results from a deliberate attempt to raise the mind to a higher, more purified level of awareness.
The commentaries define samadhi as the centring of the mind and mental factors rightly and evenly on an object. Samadhi, as wholesome concentration, collects together the ordinarily dispersed and dissipated stream of mental states to induce an inner unification. The two salient features of a concentrated mind are unbroken attentiveness to an object and the consequent tranquillity of the mental functions, qualities which distinguish it from the unconcentrated mind. The mind untrained in concentration moves in a scattered manner which the Buddha compares to the flapping about of a fish taken from the water and thrown onto dry land. It cannot stay fixed but rushes from idea to idea, from thought to thought, without inner control. Such a distracted mind is also a deluded mind.
Overwhelmed by worries and concerns, a constant prey to the defilements, it sees things only in fragments, distorted by the ripples of random thoughts. But the mind that has been trained in concentration, in contrast, can remain focused on its object without distraction. This freedom from distraction further induces a softness and serenity which make the mind an effective instrument for penetration. Like a lake unruffled by any breeze, the concentrated mind is a faithful reflector that mirrors whatever is placed before it exactly as it is.
BY BHIKKHU BODHI