Hetu: 'cause', condition, reason; Abhidhamma root-condition. In sutta usage it is almost synonymous with paccaya 'condition', and often occurs together with it 'What is the cause, what is the condition', ko hetu ko paccayo.
In Abhidhamma, it denotes the advantageous and disadvantageous roots mūla. In that sense, as 'root-condition' hetu-paccaya see. paccaya it is the first of the 24 conditions given in the introduction to the Patthāna see: Guide, p. 117. The Dhs 1052-1082 and Patthāna Duka-patth; Guide, p. 144 have sections on roots hetu. - The term is also used a for the classification of consciousness, as sa-hetuka and a-hetuka with and without concomitant root-conditions; b for a division of rebirth consciousness into ahetuka dvihetuka and tihetuka without, with 2, or with 3 root-conditions.
Maha Thera Nyanatiloka. Manual of Buddhist Terms and Doctrines, Buddhist Publication Society, first edition 1952.