'morality', 'virtue', is a mode of mind and volition (cetana) manifested in speech or bodily action (s. karma). It is the foundation of the whole Buddhist practice, and therewith the first of the 3 kinds of training (sikkhā) that form the 3-fold division of the 8-fold Path (s. magga), i.e. morality, concentration and wisdom.
Buddhist morality is not, as it may appear from the negative formulations in the Sutta-texts, something negative. And it does not consist in the mere not committing of evil actions, but is in each instance the clearly conscious and intentional restraint from the bad actions in question and corresponds to the simultaneously arising volition.
Morality of the 8-fold Path, namely, right speech, right action and right livelihood, is called 'genuine or natural morality' pakatisīla), as distinguished from the external rules for monks or laymen, the so-called 'prescribed morality' (paññatti-sīla, q.v.), which, as such, is karmically neutral.
"What now is karmically wholesome morality (kusala-sīla)? It is the wholesome bodily action (kāya-kamma, s. karma), wholesome verbal action (vacī-kamma, s. karma), and also the purity with regard to livelihood which I call morality" (M. 78). Cf. magga, 3-5.
For the 5, 8 and 10 rules, s. sikkhāpada. Further cf. cāritta- and vāritta-sīla.
The 4 kinds of morality consisting of purification (catupārisuddhi-sīla) are:
(1) restraint with regard to the monks' Disciplinary Code,
(2) restraint of the senses,
(3) purification of livelihood,
(4) morality with regard to the 4 requisites (of the monk) .
(1) Restraint with regard to the Disciplinary Code (pātimokkha-samvara-sīla). "Here the monk is restrained in accordance with the monks' Disciplinary Code, is perfect in conduct and behaviour, and perceiving danger even in the least offences, he trains himself in the rules he has taken upon him" (A . V, 87,109 ,114, etc. ) .
(2) Restraint of the senses (indriya-samvara-sīla). "Whenever the monk perceives a form with the eye, a sound with the ear, an odour with the nose, a taste with the tongue, an impression with the body, an object with the mind, he neither adheres to the appearance as a whole, nor to its parts. And he strives to ward off that through which evil and unwholesome things, greed and sorrow, would arise, if he remained with unguarded senses; and he watches over his senses, restrains his senses" (M 38).
(3) Purification of livelihood (ājīva-pārisuddhi-sīla). It consists therein that the monk does not acquire his livelihood in a way unbefitting to a monk.
(4) Morality with regard to the 4 requisites (paccaya-sannissita-sīla). It consists therein that the monk is guided by the right mental attitude when making use of the 4 requisites: robes, alms food, dwelling and medicine. "Wisely reflecting he makes use of his robes ... merely to protect himself against cold and heat, etc. Wisely reflecting he makes use of his alms food... merely as a prop and support to this body.... Wisely reflecting he makes use of his dwelling... merely to keep off the dangers of weather and to enjoy solitude.... Wisely reflecting he makes use of the necessary medicines, merely to suppress feelings of sickness that arise, and to reach perfect freedom from suffering" (cf. M. 2).
About these 4 kinds of morality, Vis.M. I gives a detailed exposition.