conceptual groupings of physical and mental processes, which are called "dhammas". Examples of lists of dhammas taught by the Buddha include the twelve sense 'spheres' or ayatanas, the five aggregates or khandha and the eighteen elements of cognition or dhatus. Theravāda traditionally promotes itself as the Vibhajjavāda "teaching of analysis" and as the heirs to the Buddha's analytical method. Expanding this model, Theravāda Abhidhamma scholasticism concerned itself with analyzing "ultimate truth" (paramattha-sacca) which it sees as being composed of all possible dhammas and their relationships. The central theory of the Abhidhamma is thus known as the "dhamma theory". "Dhamma" has been translated as "factors" (Collett Cox), "psychic characteristics" (Bronkhorst), "psycho-physical events" (Noa Ronkin) and "phenomena" (Nyanaponika Thera). According to the Sri Lankan scholar Y. Karunadasa, a dhammas ("principles" or "elements") are "those items that result when the process of analysis is taken to its ultimate limits". However, this does not mean that they have an independent existence, for it is "only for the purposes of description" that they are postulated. Noa Ronkin defines dhammas as "the constituents of sentient experience; the irreducible 'building blocks' that make up one's world, albeit they are not static mental contents and certainly not substances." Thus, while in Theravāda Abhidhamma, dhammas are the ultimate constituents of experience, they are not seen as substances, essences or independent particulars, since they are empty (suñña) of a self (attā) and conditioned. This is spelled out in the Patisambhidhamagga, which states that dhammas are empty of svabhava (sabhavena suññam). According to Ronkin, the canonical Pāli Abhidhamma remains pragmatic and psychological, and "does not take much interest in ontology" in contrast with the Sarvastivada tradition. Paul Williams also notes that the Abhidhamma remains focused on the practicalities of insight meditation and leaves ontology "relatively unexplored". Ronkin does note however that later Theravāda sub-commentaries (ṭīkā) do show a doctrinal shift towards ontological realism from the earlier epistemic and practical concerns. On the other hand, Y. Karunadasa contends that the tradition of realism goes back to the earliest discourses, as opposed to developing only in later Theravada sub-commentaries: If we base ourselves on the Pali Nikayas, then we should be compelled to conclude that Buddhism is realistic. There is no explicit denial anywhere of the external world. Nor is there any positive evidence to show that the world is mind-made or simply a projection of subjective thoughts. That Buddhism recognizes the extra-mental