Bojjhanga: ‘the 7 factors of enlightenment’, are: awareness or mindfulness sati-sambojjhanga, sati, investigation of the law dhamma-vicaya-sambojjhanga energy viriya-sambojjhanga, viriya padhāna rapture pīti - sambojjhanga tranquillity passaddhi - sambojjhanga, concentration samādhi-sambojjhanga, equanimity upekkhā. Because they lead to enlightenment, therefore they are called factors of enlightenment see: XLVI, 5.
Though in the 2nd factor, dhamma - vicaya the word dhamma is taken by most translators to stand for the Buddhist doctrine, it probably refers to the bodily and mental phenomena nāma - rūpa - dhammā as presented to the investigating mind by awareness or mindfulness, the 1st factor. With that interpretation, the term may be rendered by ‘investigation of phenomena’.
In A. X. 102, the 7 factors are said to be the means of attaining the threefold understanding see: tevijjā.
They may be attained by means of the 4 foundations of awareness or mindfulness satipatthāna,, as it is said in see: XLVI, 1 and explained in M. 118:
1: Whenever, o Bhikkhus, the Bhikkhu dwells contemplating the body kāya feeling vedanā mind citta and mental-objects dhammā strenuous, clearly-conscious, mindful, after subduing worldly greed and grief, at such a time his awareness or mindfulness is present and undisturbed; and whenever his awareness or mindfulness is present and undisturbed, at such a time he has gained and is developing the link to Awakening ‘awareness or mindfulness’ sati-sambojjhanga and thus this link to Awakening reaches fullest perfection.
2: Whenever, while dwelling with awareness or mindfulness, he wisely investigates, examines and thinks over the law… at such a time he has gained and is developing the link to Awakening ‘investigation of the law’ dhamma - vicaya °…
3: Whenever, while wisely investigating his energy is firm and unshaken… at such a time he has gained and is developing the link to Awakening ‘energy’ viriya…
4: Whenever in him, while firm in energy, arises supersense-rapture… at such a time he has gained and is developing the link to Awakening ‘rapture’ pīti °.
5: Whenever, while enraptured in mind, his body and his mind become composed… at such a time he has gained and is developing the link to Awakening ‘tranquillity’ passaddhi °
6: Whenever, while being composed in his body and happy, his mind becomes concentrated… at such a time he has gained and is developing the link to Awakening ‘concentration’ samādhi °
7: Whenever he looks with complete indifference on his mind thus concentrated… at such a time he has gained and is developing the link to Awakening ‘equanimity’ upekkhā.
Literature: Bojjhanga Samyutta see: XLVI; Bojjhanga Vibh. - For the conditions leading to the arising of each of the factors, see the Com. to Satipatthāna Sutta Way of Mindfulness, by Soma Thera; 3rd ed., 1967, BPS. Further, The ’Seven Factors of Enlightenment, by Piyadassi Thera WHEEL 1.