  In the schematic analysis of the five aggregates only form is a physical aggregate stricto sensu. While sensations, apperception, and volitions can acquire an objectual aspect, they are not empirical objects proper. Thus, a sensation such as pain is not reducible to the physical substrate, say a finger, in which it is instantiated. Rather, as object-oriented cognitive aspects, sensations, apperception, and volitions are included in the broader Abhidharma category of mental factors (caitasika). Furthermore, the empirical approach that characterizes the Buddhist analysis of materiality does not imply physicalism, at least not in the sense that everything is or supervenes on the physical. Rather, materiality is analyzed as being reducible to the phenomenal content of experience. Thus, the formal properties of material objects are analyzed either in terms of how they are impacted by contact or as factors that oppose resistance. These properties, however, do not extend to the atoms themselves, which according to the Abhidharma form the building blocks of materiality. As monadic units the atoms are seen as devoid of any formal properties (rūpaṇa). It is only as atomic compounds (saṃghātastha, saṃcita) that atoms are subject to the same properties of resistance and destruction as composite material entities (see   §4.2).  