'the 7 factors of enlightenment', are:
"Because they lead to enlightenment, therefore they are called factors of enlightenment" (S. 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 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 wisdom (s. tevijjā).
They may be attained by means of the 4 foundations of mindfulness (satipatthāna), as it is said in S.XLVI.1 and explained in M.118:
(1) "Whenever, o monks, the monk dwells contemplating the body (kāya), feeling (vedanā), mind (citta) and mind-objects (dhammā), strenuous, clearly-conscious, mindful, after subduing worldly greed and grief, at such a time his mindfulness is present and undisturbed; and whenever his mindfulness is present and undisturbed, at such a time he has gained and is developing the factor of enlightenment 'mindfulness' (sati-sambojjhanga), and thus this factor of enlightenment reaches fullest perfection.
(2) "Whenever, while dwelling with mindfulness, he wisely investigates, examines and thinks over the law ... at such a time he has gained and is developing the factor of enlightenment '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 factor of enlightenment 'energy' (viriya°) ....
(4) "Whenever in him, while firm in energy, arises super sensuous rapture ... at such a time he has gained and is developing the factor of enlightenment '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 factor of enlightenment '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 factor of enlightenment '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 factor of enlightenment 'equanimity' (upekkhā).
Literature:
Bojjhanga Samyutta (S. 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).
The 'Seven Factors of Enlightenment, by Piyadassi Thera (WHEEL 1.)