An important theory held by some Sarvāstivādins, Theravādins and Sautrāntikas was the theory of "momentariness" (Skt., kṣāṇavāda, Pali, khāṇavāda). This theory held that dhammas only last for a minute moment ("ksana") after they arise. The Sarvāstivādins saw these 'moments' in an atomistic way, as the smallest length of time possible (they also developed a material atomism). Reconciling this theory with their eternalism regarding time was a major philosophical project of the Sarvāstivāda. The Theravādins initially rejected this theory, as evidenced by the Khaṇikakathā of the Kathavatthu which attempts to refute the doctrine that "all phenomena (dhamma) are as momentary as a single mental entity." However, momentariness with regards to mental dhammas (but not physical or rūpa dhammas) was later adopted by the Sri Lankan Theravādins, and it is possible that it was first introduced by the scholar Buddhagosa.