Yes. You are correct that only the four maha bhuta are mentioned as components of the ‘fundamental element of matter’ in the suttas. In fact, the suttas do not use the word suddhāṭṭhaka for that ‘fundamental element of matter.’
- That is because Abhidhamma was not taught (or even fully developed) during the lifetime of the Buddha. The Buddha taught the essential elements to Ven. Sariputta, and ‘his lineage of bhikkhus‘ developed the Abhidhamma theory over many generations. It was finalized about 200 years after the Buddha’s passing. See “Abhidhamma – Introduction.”
- The eight elements in a suddhāṭṭhaka are discussed in “The Origin of Matter – Suddhāṭṭhaka.” The following is in that post:
Suddhāṭṭhaka (“suddha” for “pure” or fundamental” + “aṭṭha” or “eight”) means a unit of matter consisting of eight fundamental entities (usually translated as the ‘pure octad’).
- Four of these belong to the “bhūta” stage of pathavi, āpo, tejo, and vāyo arising due to avijjā.
- The craving for material things leads to four more due to taṇhā. Those are vaṇṇa, gandha, rasa, and oja are created due to taṇhā. The four upādāya rūpa are based on tanha that you mentioned (as the suttas refer to) are these four.
- Since Abhidhamma was not taught during the time of the Buddha, the four units arising due to tanha were only referred to as ‘upādāya rūpa.’
P.S. The word ‘upādāya‘ is related to ‘upādāna‘ and thus, tanha.
