[623] "'The eighteen mental explorations (manopavicāra) should be understood' — so indeed was this said. In dependence on what was this said?
Having seen a form (rūpa) with the eye, one explores a form that is a basis for joy (somanassa), one explores a form that is a basis for grief (domanassa), one explores a form that is a basis for equanimity (upekkhā).
Having heard a sound with the ear ...
Having smelled an odor with the nose ...
Having tasted a flavor with the tongue ...
Having touched a tangible with the body ...
Having cognized a dhamma with the mind, one explores a dhamma that is a basis for joy, one explores a dhamma that is a basis for grief, one explores a dhamma that is a basis for equanimity.
Thus there are six explorations with joy, six explorations with grief, and six explorations with equanimity. So when it was said, 'The eighteen mental explorations should be understood,' it was in dependence on this that it was said.
English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.