'elements', are the ultimate constituents of a whole.
(1) The 4 physical elements (dhātu or mahā-bhūta), popularly called:
are to be understood as the primary qualities of matter.
In Vis.M. XI, 2 the four elements are defined thus:
"Whatever is characterized:
All four are present in every material object, though in varying degrees of strength. If, for instance, the earth element predominates, the material object is called 'solid', etc. - For the analysis of the 4 elements, s. dhātu-vavatthāna.
(II) The 18 physical and mental elements that constitute the conditions or foundations of the process of perception, are:
1-10 are physical; 11-16 and 18 are mental; 17 may be either physical or mental.
16 performs the function of advertence (āvajjana) towards the object at the inception of a process of sensuous consciousness; it further performs the function of receiving (sampaticchana) the sensuous object.
18 performs, e.g., the function of investigation (santīrana), determining (votthapana) and registering (tadārammana) - (for its other functions, s. Table I).
For the 14 functions of consciousness, s. viññāna-kicca.
Cf. M. 115; S. XIV and especially Vibh. II (Guide p. 28f), Vis.M. XV, 17ff.
Of the many further groupings of elements (enumerated in M.115), the best known is that of the 3 world-elements:
further the six-fold group: