Kusala: 'kammically advantageous' or 'profitable', salutary, morally good, skillful Connotations of the term, according to Com. Atthasālini, are: of good health, blameless, productive of favourable kamma-result, skillful. It should be noted that Com. excludes the meaning 'skillful', when the term is applied to states of consciousness.
It is defined in M. 9 as the 10 advantageous courses of action see: kamma-patha In psychological terms, 'kammically advantageous' are all those kammical intentions kamma-cetanā and the consciousness and mental properties associated therewith, which are accompanied by 2 or 3 advantageous roots see: mūla i.e. by greedlessness alobha and hatelessness adosa and in some cases also by non-confusion amoha understanding, understanding. Such states of consciousness are regarded as 'kammically advantageous' as they are causes of favourable kamma results and contain the seeds of a happy destiny or rebirth. From this explanation, two facts should be noted: 1 it is intention that makes a state of consciousness, or an act, 'good' or 'bad'; 2 the moral criterion in Buddhism is the presence or absence of the 3 advantageous or moral roots see: mūla
The above explanations refer to mundane lokiya advantageous consciousness. supra-mundane advantageous lokuttara-kusala states, i.e. the four paths of sanctity see: ariya-puggala have as results only the corresponding four fruitions; they do not constitute kamma, nor do they lead to rebirth, and this applies also to the good actions of an Arahat Tab. I, 73-80 and his meditative states Tab. 1, 81-89, which are all kammically inoperative functional; s. kiriya
kusala belongs to a threefold division of all consciousness, as found in the Abhidhamma Dhs., into advantageous kusala disadvantageous akusala and kammically neutral avyākata which is the first of the triads tika in the Abhidhamma schedule mātikā see: Guide, pp. 4ff., 12ff; Vis.M XIV, 83ff.
Maha Thera Nyanatiloka. Manual of Buddhist Terms and Doctrines, Buddhist Publication Society, first edition 1952.